THE 

,<«?*. 


UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


IFOKNV 


STATE  NORMALSCHOOL, - 

LOS  AKOELE3,  -•-  OAL. 


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THE  INTERNATIONAL  SCIENTIFIC  SERIES 

VOLUME   LXVII 


THE 

INTERNATIONAL  SCIENTIFIC  SERIES. 


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The  International  Scientific  Seri«»-(Continued.) 


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>!  COMPARATIVE  LITERATURE.  By  HCTCHESOX  MACAULAY  POBNKTT, 
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91.  ANTHROPOLOGY.  An  Introduction  to  the  Study  of  Man  and  Civilization. 
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63.  THE  ORIGIN  OF  FLORAL  STRUCTURES,  THROUGH  INSECT  AND 

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WITH  SPECIAL  REFERENCE  TO  INSECTS.    By  Sir  JOHN  LUBBOCK. 
With  ovrr  100  Illustrations.    $1.75. 

65.  THE   PRIMITIVE    FAMILY   IN  ITS  ORIGIN    AND    DEVELOPMENT. 

By  Dr.  C.  N.  STABCKE,  of  the  University  of  Copenhagen. 

66.  PHYSIOLOGY  OF  BODILY  EXERCISE.    By  FEBNAND  LAGBANQK,  M.  D. 

67.  THE  COLOURS  OF  ANIMALS:  Their  Meaning  and  Use.    By  EDWABD 

BAGNALL  POULTON,  F.  R.8. 


MIMICRY  IN  SOUTH  AFRICAN  BUTTERFLIES. 

KlGCRKS    1,    4,    AND   5,    THK    FEMALES    OF    A    SoUTH    AFRICAN    PafiKo,    TOTALLY    UNLIKE    THE    MAI 
(FlGHHB  iX  BltT    MIMICKING    RESPECTIVELY  THREE  SPECIF.S  OF  THE   UNPALATABLE  GENUS,  DdnaiS  (FlGURl 

3*,-  4a,  AND  sa)     THE  FEMALE  (FIGURE  2)  OF  A  NEARLY  ALUHD  Papilla,  IN  MADAGASCAR,  is  NOT  MIMETI 

AND  RKSEMHLES  THE  HALE. 


DESCBIPTION  OF  PLATE 


THE  figures  have  been  copied,  by  kind  permission  of  the  author,  and 
the  council  of  the  Linnean  Society,  from  the  plates  accompany- 
ing Mr.  Koland  Trimen's  paper,  '  On  some  Remarkable  Mimetic 
Analogies  among  African  Butterflies.'  ('Linn.  Soc.  Trans.'  vol. 
xxvi.  pp.  497,  et  seqq.) 

All  figures  are  represented  one-half  of  their  natural  size.  The 
appearance  of  the  under  side  of  the  wings  is  shown  on  the  left  hand 
of  the  four  upper  figures. 

Figure  1. — The  male  of  Papilio  merope  (now  called  P.  cenea ;  the 
name  P.  merope  being  restricted  to  the  West  African  form),  from 
Knysna,  Cape  Colony.  A  closely  allied  butterfly  (P.  meriones), 
with  a  very  similar  male,  is  found  in  Madagascar. 
Figure  2. — The  female  of  Papilio  meriones,  from  Madagascar.  The 
male  is  almost  exactly  like  Figure  1.  The  black  bar  on  the  costal 
margin  of  the  fore  wing  of  the  female  probably  represents  the 
beginning  of  the  darkening  which  has  been  carried  so  far  in  the 
females  of  the  African  P.  merope  and  P.  cenea. 
Figure  3. — First  or  cenea-torm  of  female  of  Papilio  merope  (now 
called  P.  cenea),  from  Knysna,  Cape  Colony.  The  female  is  totally 
unlike  the  male  of  the  same  species  (Figure  1),  but  closely  mimics 
an  unpalatable  butterfly,  Danais  echeria,  prevalent  in  its  locality. 
The  appearance  of  the  latter  is  shown  in  Figure  Ba.  The  mimetic 
resemblance  is  seen  to  be  very  striking  on  both  upper  and  under 
sides  of  the  wings.  A  local  variety  of  the  Danais  is  also 
mimicked  by  a  corresponding  variety  of  the  Papilio. 
Figure  4.— Second  or  hippocoon-form  of  female  of  Papilio  merope 
(now  called  P.  cenea),  from  Graham's  Town,  Cape  Colony.  This 
variety  mimics  the  southern  form  of  the  unpalatable  Danais 
niavius,  shown  in  Figure  4a. 

Figure  5. --Third  or  tropJionius-tona.  of  female  of  Papilio  merope 
(now  called  P.  cenea),  from  Knysna,  Cape  Colony.  This  variety 
mimics  the  abundant  and  unpalatable  Danais  chrysippus  shown 
in  Figure  5a. 

In  a  closely  allied  species  of  Papilio  from  West  Africa  (the  true 
Papilio  merope)  the  male  closely  resembles  Figure  1,  while  there  are 
two  mimetic  varieties  of  female.  The  hippocoon-iorm  is  like  Figure  4, 
except  that  it  is  larger  and  the  white  patch  on  the  hind  wing 
is  smaller  ;  corresponding  in  both  these  respects  to  the  West  African 
variety  of  Danais  niavius.  The  trophonitis-torm  resembles  Figure  5. 
There  is  no  cenea-torm  of  this  species.  For  further  details  see 
pp.  234-38. 


THE   INTERNATIONAL   SCIENTIFIC  SERIES 


THE 


COLOURS  OF  ANIMALS 


THEIR  MEANING  AND  USE,  ESPECIALLY  CONSIDERED 
IN  THE  CASE  OF  INSECTS 


BY 

EDWARD  BAGNALL  POULTON,  M.A.,  F.R.S. 


WITH  CHROMOLITHOGRAPHS  FRONTISPIECE 
AND  SIXTY-SIX  FIGURES  IN  TEXT 


NEW   YORK 
D.   APPLETON    AND    COMPANY 

1890 

son 


Qu 


PEEFACB 


I  HAVE  adopted  a  general  title,  'The  Colours  of 
Animals,'  in  order  to  indicate  the  contents  of  this 
volume,  although  the  vast  majority  of  the  examples 
are  taken  from  insects,  and  indeed  almost  invariably 
from  a  single  order,  the  Lepidoptera.  The  examples 
are,  however,  employed  merely  to  illustrate  principles 
which  are  of  wide  appli cation. 

I  have  purposely  abstained  from  multiplying  in- 
stances when  a  little  observation  or  even  reflection 
will  supply  them  in  large  numbers.  For  example, 
the  ordinary  Protective  Resemblances  of  mammals 
and  birds  are  barely  alluded  to,  on  this  account.  On 
the  other  hand,  more  difficult  problems,  such  as  the 
change  of  colour  in  arctic  mammals,  or  the  meaning 
of  the  colours  of  birds'  eggs,  are  treated  at  far  greater 
length.  My  object  in  both  cases  is  the  same  :  to 
stimulate  observation  in  a  subject  which  will  amply 
repay  investigation,  from  the  scientific  value  of  the 
results,  and  the  never-failing  interest  and  charm  of 
the  inquiry. 


viii  THE  COLOURS  OF  ANIMALS 

Variable  Protective  Eesemblance  in  insects  is 
treated  in  considerable  detail,  for  the  reasons  given 
above,  and  because  much  of  the  work  is  so  recent 
that  no  complete  account  can  be  found  outside  the 
original  memoirs. 

My  chief  object  has  been  to  demonstrate  the 
utility  of  colour  and  marking  in  animals.  In  many 
cases  I  have  attempted  to  prove  that  Natural  Selection 
has  sufficed  to  accouDt  for  the  results  achieved ;  and 
I  fully  believe  that  further  knowledge  will  prove  that 
this  principle  explains  the  origin  of  all  appearances 
except  those  which  are  due  to  the  subordinate  prin- 
ciple of  Sexual  Selection,  and  a  few  comparatively 
unimportant  instances  which  are  due  to  Isolation  or 
to  Correlation  of  Growth. 

In  support  of  these  views  I  have  endeavoured  to 
bring  together  a  large  amount  of  experimental  evi- 
dence in  favour  of  the  theories  as  to  the  various  uses  of 
colour.  'Further  experiments  are  still  greatly  needed. 

In  the  chapters  on  '  Sexual  Selection '  I  have 
argued  in  favour  of  Darwin's  views,  and  have 
attempted  to  defend  them  against  recently  published 
attacks. 

At  the  conclusion  of  the  volume  I  have  brought 
forward  a  detailed  classification  of  the  various  uses 
of  colour,  in  which  new,  and,  I  believe,  more  con- 
venient terms  are  suggested.  Definitions  and  exam- 
ples are  also  given  in  the  classification,  which  is,  in 
fact,  a  brief  abstract  of  the  whole  book. 


PEEFACE  IX 

I  have  to  thank  the  Councils  of  various  scientific 
societies  for  the  courteous  permission  to  copy  figures 
from  their  respective  publications.  The  figures  in 
the  coloured  plate  are  copied  from  the  plates  accom- 
panying Mr.  Eoland  Trimen's  paper  in  the  '  Trans- 
actions of  the  Linnean  Society,'  vol.  xxvi.  pp. 
497-522.  Figures  18,  19,  20,  21,  and  22  are  copied 
from  the  plate  accompanying  Mr.  E.  Bowdler  Sharpe's 
paper  in  the  '  Proceedings  of  the  Zoological  Society,' 
1873,  pp.  414  et  seqq.  Figures  3,  4,  5,  6,  7,  8,  11, 
14,  58,  60,  61,  62  are  copied  from  the  plates  and 
woodcuts  accompanying  my  papers  in  the  '  Transac- 
tions of  the  Entomological  Society,'  1884, 1885,  1887, 
and  1888.  Figures  25,  26,  and  27  are  copied  from 
the  plate  accompanying  Mrs.  Barber's  paper  in  the 
'  Transactions  of  the  Entomological  Society,'  1874, 
pp.  519  et  seqq.  Figures  29  and  30  are  copied  from 
the  plate  and  woodcuts  accompanying  my  paper  in 
the  '  Philosophical  Transactions  of  the  Eoyal  Society,' 
vol.  178  (1887),  B,  pp.  311-441.  Figures  15,  16,  53, 
54,  63,  64,  65,  66  are  copied  from  the  woodcuts  and 
plates  accompanying  G.  W.  and  E.  G.  Peckham's 
paper  in  the  '  Occasional  Papers  of  the  Natural 
History  Society  of  Wisconsin,'  vol.  i.  (1889),  Milwaukee. 
Figures  55  and  56  are  copied  from  the  plates  accom- 
panying Professor  Weismann's  '  Studies  in  the  Theory 
of  Descent,'  translated  by  Professor  Meldola.  Figure 
10  is  copied  from  one  of  the  plates  accompanying  Dr. 
Wilhelm  Midler's  '  Siidamerikanische  Nymphaliden- 


X  THE  COLOURS  OF  ANIMALS 

raupen'  ('  Zoologische  Jahrbiicher,'  J.  W.  Spengel, 
Jena,  1886).  Figure  42  is  copied  from  Vogt  ('  The 
Natural  History  of  Animals ' :  English  translation : 
Blackie  and  Son).  Figures  44  and  45  are  copied 
from  the  plates  accompanying  Curtis's  'British 
Lepidoptera.'  The  remaining  figures  are  original. 
Figure  17  was  kindly  lent  me  by  Dr.  A.  K.  Wallace, 
to  whom  it  had  been  sent  by  Mr.  Wood-Mason.  In 
preparing  the  drawings  of  the  original  figures  I  have 
been  greatly  assisted  by  my  wife,  my  sister  Miss  L.  S. 
Poulton,  Miss  Herman  Fisher,  Mr.  Alfred  Sich, 
Mr.  Alfred  Robinson,  and  especially  by  Miss  Cundell. 
I  have  almost  invariably  referred  to  original 
papers  from  which  facts  or  conclusions  have  been 
adopted;  so  that  any  reader  having  access  to  a 
scientific  library  may  easily  gain  possession  of  further 
details.  Not  wishing  to  overburden  the  book  with 
such  notes,  I  have  abstained  from  referring  constantly 
to  my  own  papers,  although  most  of  the  examples  are 
taken  from  them.  A  list  of  my  papers  which  deal 
with  the  colours  of  insects  is  therefore  printed  below. 

•Transactions  Entomological  Society,'  London,  1884,  pp.  27-60 

1885,  „  281-329 

1886,  „  137-179 

»»  »  „  „        1887,   „  281-321 

*  ..  >.  „        1888,  „  515-606 

•  Philos.  Trans.  Royal  Society,'  vol.  178  (1887),  B,  pp.  311-441 
Abstract  of  the  above  in  'Proceedings  Royal  Society,'  1887,  vol.  xlii. 

pp.  94-108 
'  Proceedings  Royal  Society,'  1885,  vol.  xxxviii.  pp.  269-315 

1886,  vol.  xl.  pp.  135-173 
'  Proceedings  Zoological  Society,'  1887,  pp.  191-274 


PEEFACE  Xi 

Short  papers  or  notes  (exclusive  of  those  which 
are  mere  abstracts  of  the  above)  : — 

'  Proceedings  Entomological  Society,' London,  1887,  pp.  1-li 

„      1887,    „   Ixi-lxii 
„  „       1888,  p.  v 

»>  »>  >»  »»          >»     PP-  viii— x 

„  „  „  „         „      „  xxvii-xxviii 

„       1889  „  xxxvii-xl 
'  Journal  of  the  Victoria  Institute,'  1888,  vol.  xxii.,  '  On  Mimicry.' 

It  is  my  pleasant  duty  to  thank  many  friends  for 
their  kind  assistance.  I  owe  to  Professor  Meldola 
more  than  I  can  possibly  express :  his  writings  first 
induced  me  to  enter  upon  this  line  of  investigation, 
and  I  have  had  the  benefit  of  his  great  experience 
and  wise  advice  during  the  whole  of  the  time  that  I 
have  been  at  work.  Nearly  every  subject  touched 
upon  in  this  volume  has  been  discussed  with  him. 

Professor  Westwood  has  always  been  most  kind 
in  helping  me  with  the  literature  of  the  subject,  with 
which  he  has  so  intimate  an  acquaintance,  and  in 
giving  me  the  free  use  of  the  Hope  collection  at 
Oxford.  Professor  E.  Eay  Lankester  has  read  the 
proof-sheets  dealing  with  the  classifications  of  the 
uses  of  colour,  and  has  offered  valuable  suggestions. 
Several  beautiful  examples  were  suggested  to  me  by 
Professor  C.  Stewart.  Dr.  Giinther,  Mr.  Eoland 
Trimen,  Mr.  Oldfield  Thomas,  Mr.  E.  Bowdler  Sharpe, 
Mr.  F.  E.  Beddard,  Mr.  W.  W.  Fowler,  and  Mr.  A. 
H.  Cocks  have  been  very  kind  in  answering  questions 
upon  their  special  subjects.  Sir  John  Conroy  has 


xii  THE  COLOURS  OF  ANIMALS 

kindly  helped  me  in  explaining  the  physical  questions 
involved  in  the  first  chapter.  I  am  especially  pleased 
to  speak  of  the  help  received  from  my  former  pupils 
Mr.  W.  Garstangand  Mr.  E.  C.  L.  Perkins,  who  have 
supplied  many  valuable  instances,  which  are  specified 
in  the  volume,  where  other  kind  assistance  is  also  duly 
acknowledged. 

Although  I  have  ventured  to  disagree  with  my 
friend  Dr.  A.  R.  Wallace  upon  the  subject  of  '  Sexual 
Selection,'  I  wish  to  acknowledge  how  very  much  I 
owe  to  his  writings,  which  I  have  very  frequently 
quoted.  I  have  also  made  great  use  of  the  late 
Thomas  Belt's  extremely  interesting  and  suggestive 
'  Naturalist  in  Nicaragua.' 

Among  recent  papers  I  wish  especially  to  mention 
that  by  G.  W.  and  E.  G.  Peckham,  of  Milwaukee, 
U.S.A.  The  minute  observation  of  these  authors 
upon  the  courtship  of  spiders  of  the  family  Attidce  is 
a  model  for  investigation  in  a  subject  which  has  never 
before  been  attacked  systematically. 

Above  all,  I  should  wish  to  acknowledge,  although 
I  can  never  fully  express,  the  depth  of  my  indebted- 
ness to  the  principles  which  first  made  Biology  a 
science,  the  principles  enunciated  by  Charles  Darwin. 
It  is  common  enough  nowadays  to  hear  of  new 
hypotheses  which  are  believed  (by  their  inventors)  to 
explain  the  fact  of  evolution.  These  hypotheses  are 
as  destructive  of  one  another  as  they  are  supposed  to 
be  of  Natural  Selection,  which  remains  as  the  one 


PREFACE  xiii 

solid  foundation  upon  which  evolution  rests.  I  have 
wished  to  express  this  conviction  because  my  name 
has  been  used  as  part  of  the  support  for  an  opposite 
opinion,  by  an  anonymous  writer  in  the  '  Edinburgh 
Eeview.'1  In  an  article  in  which  unfairness  is  as 
conspicuous  as  the  prejudice  to  which  it  is  due,  I  am 
classed  as  one  of  those  '  industrious  young  observers ' 
who  '  are  accumulating  facts  telling  with  more  or  less 
force  against  pure  Darwinism.' 2  On  the  strength  of 
this  and  other  almost  equally  strange  evidence,  the 
Eeviewer  triumphantly  exclaims,  '  Darwin,  the  thanes 
fly  from  thee  ! '  In  view  of  this  public  mention  of  my 
name,  I  may  perhaps  be  excused  for  making  the  per- 
sonal statement  that  any  scientific  work  which  I  have 
had  the  opportunity  of  doing  has  been  inspired  by 
one  firm  purpose — the  desire  to  support,  in  however 
small  a  degree,  and  to  illustrate  by  new  examples, 
those  great  principles  which  we  owe  to  the  life  and 
writings  of  Charles  Darwin,  and  especially  the  pre- 
eminent principle  of  Natural  Selection. 

E.  B.  P. 
OXFORD  :  Dec.  28,  1889. 


1  Edinburgh  Review.    Article  V.    April  1888,  pp.  407-47. 

*  p.  443.  The  bias  of  the  writer  appears  in  a  most  singular 
manner  upon  this  page.  In  the  short  space  of  seventeen  lines  the 
following  adjectives  are  divided  between  five  writers  and  their  works  — 
industrious,  illustrious,  gifted,  well-read,  acute,  intelligent,  brilliant, 
thoughtful.  I  need  hardly  say  that  all  five  writers  are  believed  by 
the  Reviewer  to  oppose  the  theory  of  Natural  Selection. 


CONTENTS 


CHAPTER  PAGE 

I.    THE  PHYSICAL  CAUSE  OF  AKIMAL  COLOURS    ...  1 

II.    THE  USES  OF  COLOUR 12 

III.  PROTECTIVE  KESEMBLANCES  IN  LEPIDOPTEBA  ...  24 

IV.  PROTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA  (continued) 

— DIMORPHISM,  ETC 42 

V.    PROTECTIVE  RESEMBLANCES  IN  VERTEBRATA,  ETC.   .        .  60 

VI.    AGGRESSIVE  RESEMBLANCES — ADVENTITIOUS  PROTECTION  72 
VII.    VARIABLE    PROTECTIVE  RESEMBLANCE    IN   VERTEBRATA, 

ETC 81 

VIII.    VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS       .     .  110 
IX.    VARIABLE   PROTECTIVE   RESEMBLANCE  m  INSECTS  (con- 
tinued)        133 

X.    WARNING  COLOURS 159 

XI.     WARNING  COLOURS  (continued) 189 

XII.    PROTECTIVE  MIMICRY 216 

XIII.  PROTECTIVE  AND  AGGRESSIVE  MIMICRY  ....  245 

XIV.  THE  COMBINATION  OF  MANY  METHODS  OF  DEFENCE       .  269 
XV.     COLOURS  PRODUCED  BY  COURTSHIP             .        .        .     .  284 

XVI.    OTHER  THEORIES  OF  SEXUAL  COLOURING       .        .        .  314 

XVII.    SUMMARY  AND  CLASSIFICATION 336 


THE 

COLOURS    OP   ANIMALS 

CHAPTER  I 
THE  PHYSICAL   CAUSE   OF  ANIMAL   COLOUBS 

Colours  due  to  absorption 

THE  colours  of  animals  are  produced  in  various  ways. 
By  far  the  commonest  method  is  the  absorption  of 
certain  elements  of  light  by  means  of  special  sub- 
stances which  are  called  pigments,  or  colouring  matters. 
The  colour  of  each  pigment  is  due  to  those  elements 
of  the  light  which  it  does  not  absorb,  and  which  can 
therefore  emerge  and  affect  the  eye  of  the  spectator. 
Black  is,  of  course,  caused  by  the  absorption  of  all 
the  constituents  of  light,  so  that  nothing  reaches  the 
eye.  The  colour  of  red  pigment,  like  that  of  red 
glass,  depends  upon  the  fact  that  red  is  less  absorbed 
than  any  other  element  of  the  light  which  passes 
through.  If  a  sheet  of  red  glass  be  placed  upon 
white  paper,  the  light  traverses  the  glass,  is  reflected 


2  THE  COLOUKS  OF  ANIMALS 

from  the  surface  of  the  paper,  re-traverses  the  glass, 
and  emerges.  Similarly,  in  painting,  bright  effects 
are  produced  by  covering  a  surface  of  Chinese  white 
with  the  desired  colour.  The  light  passing  twice 
through  the  thickness  of  the  colour,  absorption  is 
far  more  complete  than  when  only  one  thickness  is 
traversed,  as  in  a  piece  of  red  glass  held  up  to  the 
light.  Absorption  being  more  complete,  the  red  colour 
is  deeper.  Animal  pigments  are  nearly  always  twice 
traversed  by  the  light,  and  therefore  a  very  thin  layer 
produces  a  considerable  effect. 

Animal  colours  are  therefore  generally  due  to 
precisely  the  same  optical  principle  which  causes  the 
colour  of  a  wall-paper,  a  carpet,  or  a  picture.  Certain 
transparent  animals  are,  however,  for  the  most  part 
coloured  by  light  which  passes  but  once  through  them, 
upon  the  same  principle  as  the  colours  of  a  stained- 
glass  window.  The  beautiful  transparent  blue  of 
many  pelagic  animals,  such  as  the  Portuguese  Man- 
of-war  (Physalia),  is  caused  in  this  way. 

It  would  be  out  of  place  to  discuss  the  details  of 
the  causes  of  colour  by  absorption.  I  may,  however, 
mention  that  vibrations  of  very  different  rates  are 
started  in  the  luminiferous  ether  by  the  sun,  the 
electric  light,  &c.  A  certain  series  of  these  vibrations 
causes  the  effect  of  white  light  when  it  falls  on  our 
retina;  but  there  are  vibrations  above  and  below 
this  visible  series — vibrations  which  we  cannot  see. 
We  can,  however,  prove  their  existence  in  other  ways  ; 


THE  PHYSICAL  CAUSE  OF  ANIMAL  COLOURS         3 

and  it  is  certain  that  some  animals  can  see  vibrations 
which  do  not  affect  our  eyes.1  The  slowest  vibrations 
that  we  can  see,  produce  the  effect  of  red,  the  most 
rapid  the  effect  of  violet,  while  the  intermediate 
vibrations  cause  the  other  well-known  colours  of  the 
rainbow  or  the  spectrum. 

The  absorption  of  certain  elements  of  light  there- 
fore means  the  disappearance  of  ethereal  vibrations 
with  a  certain  speed.  It  is  believed  that  these 
vibrations  disappear  because  their  motion  has  been 
communicated  to  the  particles  of  the  absorbing  body. 
It  is  also  believed  that  these  particles  are  in  a  state  of 
constant  vibration,  and  that  the  vibrations  of  ether, 
which  are  timed  to  those  of  the  body,  are  used  up 
in  increasing  the  motion  of  the  latter. 

A  white  appearance  due  to  light  being  scattered 

The  production  of  white  is  due  to  a  different 
principle,  for  we  know  that  when  light  passes  through 
a  body  without  any  absorption,  the  body  is  trans- 
parent and  invisible  rather  than  white.  When  all 
the  light  passes  through,  the  body  is  completely  in- 
visible. Whiteness  is  due  to  reflection  of  the  whole 
visible  series  of  vibrations,  unaccompanied  by  the 
absorption  of  a  part  of  them,  as  in  the  production  of 
colours.  But  regular  reflection,  viz.  reflection  from 

1  Sir  John  Lubbock,  The  Senses  of  Animals,  Chapter  X.  (Inter- 
national  Scientific  Series). 


4  THE  COLOURS  OT?  ANIMALS 

a  polished  surface  like  that  of  a  mirror,  does  not 
cause  whiteness :  it  renders  the  surface  itself  invisible, 
but  produces  images  of  surrounding  objects.  A  white 
appearance  is  produced  by  irregular  reflection,  which 
causes  the  light  to  be  scattered  or  reflected  in  all 
directions.  To  produce  such  a  result  there  must 
be  an  immense  number  of  surfaces  in  an  immense 
number  of  different  directions.  If  a  coloured  sub- 
stance be  reduced  to  powder  of  various  degrees  of 
fineness,  the  colour  will  diminish  in  intensity,  and 
the  whiteness  will  increase,  according  to  the  fineness 
of  the  powder ;  this  is  because  the  number  of  re- 
flecting surfaces  is  increased,  while  the  thickness  of 
the  grains  is  diminished.  This  will  be  clear  from  the 
following  consideration.  When  a  beam  of  light  falls  on 
a  sheet  of  glass,  a  known  fraction  (about  4  per  cent.) 
of  the  light  is  reflected  back  from  the  first  surface  :  the 
larger  portion,  however,  enters  the  glass,  and,  after 
suffering  a  certain  amount  of  absorption,  reaches  the 
second  surface  and  is  again  partially  reflected.  If  the 
glass  be  powdered,  the  number  of  surfaces  will  be  so  im- 
mensely increased  that  all  the  light  will  be  reflected 
by  a  small  thickness  of  the  powder.  The  light 
reflected  from  the  second  surface  of  each  grain  of 
coloured  glass  will  still  be  coloured  by  absorption,  but 
not  sufficiently  to  produce  any  visible  results,  when 
the  thickness  of  the  grain  is  very  small. 

Reflection  is  the  immediate  cause  of  whiteness,  and 
the  amount  of  reflection  is  due  to  the  difference 


THE  PHYSICAL  CAUSE  OF  ANIMAL  COLOURS         5 

between  the  refractive  powers  (viz.  the  power  of 
changing  the  direction  of  rays  of  light)  possessed  by 
the  grains  of  glass  and  the  substance,  such  as  air  or 
water,  which  lies  between  them.  Thus  the  refractive 
powers  of  glass  and  water  are  much  nearer  than 
those  of  glass  and  air :  hence  a  dry  powder  will 
reflect  far  more  than  a  wet  one,  and  will  appear 
much  whiter. 

To  take  a  few  familiar  examples  :  snow  is  white, 
because  of  the  minute  globules  of  air  which  refract 
very  differently  from  the  crystals  between  which  they 
are  entangled  ;  ice,  on  the  other  hand,  is  transparent. 
If  snow  be  compressed  the  air  is  driven  out,  and  the 
mass  becomes  transparent ;  if  ice  be  powdered  it  be- 
comes white  like  snow.  The  froth  of  a  coloured  liquid 
is  not  coloured  like  the  latter,  but  is  white.  Milk  and 
fat  are  white  because  light  is  scattered  from  the 
surfaces  of  the  countless  oil  globules,  which  refract 
very  differently  from  the  substance  which  lies  between 
them.  The  surface  of  well-polished  glass  is  almost 
invisible,  because  it  reflects  regularly,  but  a  scratched 
surface  is  very  visible,  because  there  are  surfaces  in 
many  different  directions,  which  therefore  scatter  the 
light,  while  the  far  more  numerous  surfaces  of  ground 
glass  scatter  the  light  far  more  effectually  and  produce 
a  white  appearance. 

The  white  markings  of  animals  are  produced  in 
various  ways.  White  hairs  and  feathers  owe  their 
appearance,  like  snow,  to  the  number  of  minute 
2 


6  THE  COLOURS  OF  ANIMALS 

bubbles  of  gas  which  are  contained  in  their  inter- 
stices. Fat  is  also  made  use  of  to  give  a  white 
appearance ;  and  the  same  result  may  be  obtained  by 
the  presence  of  minute  granules,  probably  akin  to 
pigment,  but  differing  widely  from  it  in  optical  pro- 
perties, in  that  no  absorption  takes  place. 

Colours  due  to  thin  plates 

It  has  been  stated  already  that  when  light  traverses 
a  sheet  of  glass  surrounded  by  air,  a  certain  pro- 
portion of  it  is  reflected  back  at  the  first  surface  and 
a  certain  proportion  at  the  second  surface.  The 
light  will  be  reflected  in  the  same  direction  from 
both  surfaces.  It  is  believed  that  the  vibrations  of 
ether,  some  of  which  affect  us  as  light,  are  in  the  form 
of  undulations  of  different  lengths  ;  if,  therefore,  the 
sheet  of  glass  be  sufficiently  thin,  some  of  the  undula- 
tions reflected  from  the  second  surface  will  interfere 
with  those  started  from  the  first  surface.  This  will 
happen  when  the  sheet  is  of  such  a  thickness  that  the 
wave  of  light  reflected  from  the  second  surface  is  half 
an  undulation  behind  that  reflected  from  the  first 
surface ;  for  then  the  two  sets  of  undulations  will  be  in 
opposite  directions,  and  will  therefore  neutralise  each 
other. 

This  will  be  quite  clear  if  we  apply  the  same 
reasoning  to  those  visible  undulations  from  which 
the  name  itself  has  been  borrowed — the  waves  on  the 
surface  of  water.  If  a  set  of  ripples  is  started  by  the 


THE  PHYSICAL  CAUSE  OF  ANIMAL  COLOURS         7 

motion  of  an  object  in  still  water,  and  then  another 
set  is  started  from  another  object  moved,  so  that  the 
ripples  succeed  each  other  at  exactly  the  same  rate 
as  the  preceding  set,  and  if  the  second  set  is  begun 
when  the  first  has  advanced  half  a  complete  ripple 
(viz.  a  movement  up  and  down),  it  is  clear  that  the 
upward  movement  of  the  second  will  correspond  to 
the  downward  movement  of  the  first  and  vice  versa, 
so  that,  if  the  objects  are  so  placed  that  the  two  sets 
of  ripples  are  traversing  the  same  sheet  of  water, 
they  will  neutralise  and  destroy  each  other. 

If  we  compare  a  number  of  sheets  of  glass  which 
are  successively  thinner  and  thinner,  interference  will 
first  occur  among  the  longest  undulations  of  light, 
because  half  an  undulation  will  of  course  require  a 
greater  distance  (or  thickness)  than  when  the  undula- 
tions are  shorter.  As  thinner  and  thinner  sheets  are 
examined  interference  will  gradually  pass  through 
the  whole  spectrum  from  red  to  violet,  destroying 
sets  of  waves  with  shorter  and  shorter  undulations. 
The  colour  seen  in  each  case  will  be  due  to  the  other 
sets  of  waves  which  are  not  destroyed. 

The  amount  of  reflection,  and  therefore  of  inter- 
ference and  of  colour  produced,  depends  upon  the 
difference  between  the  refractive  power  of  the  thin 
sheet  and  the  substance  on  each  side  of  it. 

Such  interference  colours  are  seen  in  a  soap- 
bubble,  and  the  colours  change  as  the  bubble  be- 
comes larger  and  the  film  thinner :  they  differ,  too, 


8  THE  COLOUKS  OF  ANIMALS 

on  the  various  parts  of  the  bubble,  because  the  thin- 
ness also  varies.  A  bubble  of  melted  glass  may  be 
blown  thin  enough  to  produce  the  same  effects,  which 
are  also  well  seen  when  a  thin  layer  of  air  is  enclosed 
between  two  sheets  of  glass  or  between  the  plates  of 
some  crystals,  or  when  a  drop  of  oil  is  allowed  to 
spread  out  into  a  thin  film  on  the  surface  of  water. 
When  a  substance  has  a  laminated  structure,  and 
sufficiently  thin  films  are  enclosed  between  the  laminae, 
very  marked  effects  are  seen.  Thus  the  metallic 
appearance  of  the  laminated  flakes  which  are  formed 
on  the  surface  of  glass  which  has  been  long  buried 
in  the  earth,  is  accounted  for.  If  these  brilliant 
flakes  are  wetted  the  colour  fades  away,  because  the 
thin  films  of  air  between  the  laminas  are  displaced  by 
water,  with  a  refractive  power  much  nearer  to  that  of 
the  glass,  and  the  amount  of  reflected  light  is  there- 
fore diminished. 

Interference  colours  due  to  thin  films  are  certainly 
very  important  among  animals,  but  the  extent  to 
which  they  occur  is  imperfectly  known.  The  irides- 
cent colours  of  many  beetles'  wings  are  probably  due 
to  thin  films  of  air  included  between  layers  of  a  horny 
consistence  Such  colours  are  unaltered  in  dried 
specimens.  In  other  cases  the  chinks  between  the 
layers  are  kept  open  by  films  of  less  powerfully  re- 
fractive liquids.  When  the  tissue  becomes  dry  the 
films  evaporate  and  the  colour  disappears.  We 
must  suppose  that  the  denser  layers  come  together, 


THE  PHYSICAL  CAUSE  OF  ANIMAL  COLOUKS         9 

obliterating  the  chinks  and  excluding  the  air;  otherwise 
the  colours  would  be  more  brilliant  than  ever,  because 
the  refractive  power  of  air  is  even  lower  than  that  of 
the  liquids.  The  brilliant  metallic  appearance  of 
many  chrysalides,  especially  in  the  genus  Vanessa, 
is  caused  by  a  large  number  of  films  of  liquid  enclosed 
between  the  laminae  of  the  dense  outer  layer.  If  the 
pupa  be  kept  in  spirit  or  water  the  colour  remains, 
but  disappears  directly  it  is  dry,  although  it  can  be 
renewed  any  number  of  times  by  wetting.  This  may 
even  occur  in  a  living  animal,  for  Dr.  Sharp  has  just 
directed  my  attention  to  an  interesting  observation 
made  by  Dr.  Nickerl,  who  found  that  a  brilliantly 
golden  beetle  (Carabus  auronitens)  lost  all  its  lustre 
after  hybernating  in  captivity,  but  entirely  regained 
it  after  drinking  some  water. 

Colours  due  to  diffraction 

When  white  light  falls  upon  a  surface  on  which 
there  are  a  number  of  fine  parallel  grooves  the  re- 
flected light  appears  coloured,  the  colour  varying  with 
the  angle  at  which  the  light  falls  on  the  surface,  and 
with  the  angle  at  which  it  is  seen.  This  is  due  to  the 
light  reflected  from  different  portions  of  the  surface 
having  different  distances  to  travel  before  reaching  the 
observer :  and  when  (as  occurs  when  the  grooves  are 
very  close  together)  these  differences  amount  to  half 
a  complete  undulation  for  any  particular  length  of 
vibration,  interference  is  caused,  and  the  vibration 


10  THE  COLOURS  OF  ANIMALS 

of  that  particular  rate  is  wanting  from  the  reflected 
light,  which  therefore  appears  coloured. 

Opinions  differ  as  to  the  relative  importance  of 
animal  colours  due  to  thin  plates  and  to  diffraction. 
Many  which  were  believed  to  result  from  the  latter 
are  in  all  probability  due  to  the  former.  The  irides- 
cent colours  on  the  inner  surface  of  many  shells 
(mother-of-pearl)  are  at  any  rate  partially  caused  by 
diffraction,  for  an  accurate  cast  of  the  surface  exhibits 
traces  of  the  colours.1  The  shell  is,  however,  a 
laminated  structure,  and  the  colours  may  therefore 
in  part  be  caused  by  thin  plates. 

Colours  due  to  refraction  (prismatic  colours) 

When  light  passes  through  a  wedge-shaped  trans- 
parent substance  (or  prism)  with  greater  refractive 
power  than  the  surrounding  medium,  it  is  bent  in  the 
same  direction  at  both  surfaces,  but  its  different  con- 
stituents are  bent  unequally.  The  slowest  vibrations 
(red)  are  bent  least,  the  most  rapid  (violet)  most ;  and 
when  the  substance  possesses  a  sufficiently  high  re- 
fractive power,  all  the  colours  of  white  light  are  seen 
arranged  like  the  rays  of  a  fan  in  the  order  of  their 
rates  of  vibration.  Prismatic  colours  like  those  of  the 
diamond  are  due  to  refraction. 

1  Professor  C.  Stewart  informs  me  that  he  has  repeated  Brewster's 
original  experiment,  upon  which  the  above  statement  depends.  He 
found  that  the  colour  was  due  to  a  thin  layer  of  shell  which  had  been 
stripped  off  and  adhered  to  the  surface  of  the  wax. 


THE  PHYSICAL  CAUSE  OF  ANIMAL  COLOURS   11 

It  is  doubtful  how  far  the  colours  of  animals  are 
caused  by  this  principle ;  but  Dr.  Gadow  has  given 
strong  reasons  for  supposing  that  the  metallic 
colours  of  birds'  feathers  are  produced  in  this  way,1 
and  there  are  scales  on  the  wings-cases  of  certain 
beetles  (Pachyrhynchus)  which  also  may  owe  their 
colours  to  refraction. 

All  these  causes  of  animal  colours  may  be  conve- 
niently grouped  under  two  heads — (1)  pigmentary,  and 
(2)  structural.  The  first  head  includes  colours  caused 
by  absorption,  and  the  effects  produced  vary  with  the 
chemical  nature  of  the  substance  (pigment).  The 
second  head  includes  the  colours  or  appearances  pro- 
duced in  all  other  ways,  the  efficient  cause  being  the 
structure  of  the  substance  rather  than  its  chemical 
nature. 

1  Proc  Zool.  Soc.  1882,  pp.  409  et  ae%. 


12  THE  COLOUKS  OF  ANIMALS 


CHAPTEE  H 
THE   USES  OF  COLOUR 

I.  Non-significant  colours 

COLOUR,  as  such,  is  not  necessarily  of  any  value  to  an 
organism.  Organic  substances  frequently  possess  a 
chemical  and  physical  structure  which  causes  certain 
light-waves  to  be  absorbed ;  or  the  elements  of  tis- 
sues may  be  so  arranged  that  light  is  scattered,  or 
interference  colours  are  produced.  Thus  blood  is 
red,  fat  is  white,  and  the  external  surface  of  the  air- 
bladder  in  certain  fishes  has  a  metallic  lustre,  like 
silver.  In  such  cases  there  is  no  reason  why  we  should 
inquire  as  to  the  use  or  meaning  of  the  colour  in  the 
animal  economy ;  the  colour,  as  such,  has  no  more 
meaning  than  it  has  in  a  crystal  of  sulphate  of  copper 
or  iron.  Such  colours  are  the  incidental  results  of 
chemical  or  physical  structure,  which  is  valuable  to 
the  organism  on  its  own  account.  This  argument 
will  be  still  further  enforced  if  we  remember  that  the 
colours  in  question  are,  strictly  speaking,  not  colours 
at  all.  Blood  and  fat  are  so  constituted  that  they 
will  be  red  and  white,  respectively,  in  the  presence  of 


THE  USES   OF  COLOUR  13 

light,  but  they  cannot  be  said  to  possess  these  colours 
in  their  normal  position,  buried  beneath  the  opaque 
surface  of  an  animal. 

The  existence  of  non- significant  colours  is,  never- 
theless, most  important,  for  they  form  the  material 
out  of  which  natural  or  sexual  selection  can  create 
significant  colours.  Thus,  the  colour  of  blood  may  be 
made  use  of  for  '  complexion,'  while  fat  may  be  em- 
ployed to  produce  white  markings,  as  in  certain  insect 
larvae.  The  yellow,  brown,  and  red  fatty  matters  of 
the  connective  tissue  are  accumulated  beneath  the 
skin  in  patches,  so  as  to  produce  patterns. 

All  colour  originally  non-significant 

All  animal  colour  must  have  been  originally  non- 
significant, for  although  selective  agencies  have  found 
manifold  uses  for  colour,  this  fact  can  never  have 
accounted  for  its  first  appearance.  It  has,  however, 
been  shown  that  this  first  appearance  presents  no 
difficulty,  for  colour  is  always  liable  to  occur  as  an 
incidental  result.  This  is  even  true  of  the  various 
substances  which  seem  to  be  specially  set  apart  for  the 
production  of  colour  in  animals ;  for  pigments  occur 
abundantly  in  the  internal  organs  and  tissues  of  many 
forms.  The  brilliant  colours  of  some  of  the  lower 
organisms  are  probably  also  non-significant.  In  all 
higher  animals,  however,  the  colours  on  the  surface 
of  the  body  have  been  significant  for  a  vast  period  of 
time,  so  that  their  amount,  their  arrangement  in 


14  THE  COLOURS  OF  ANIMALS 

patterns,  their  varying  tints,  and  their  relation  to  the 
different  parts  of  the  body,  have  all  been  determined 
by  natural  selection  through  innumerable  generations. 
Because  the  origin  of  all  pigments  is  to  be  found  in 
the  incidental  result  of  the  chemical  and  physical 
nature  of  organic  compounds,  it  by  no  means  follows 
that  incidental  or  non-significant  colours  would  have 
appeared  at  all  on  the  surface  of  most  animals. 
And  we  find  as  a  matter  of  fact  that  such  colours 
tend  to  disappear  altogether,  directly  they  cease  to  be 
useful,  as  in  cave-dwelling  animals.  On  the  other 
hand,  the  non-significant  colour  of  blood  or  of  fat 
would  persist  undiminished  in  such  forms. 


Colours  may  be  destroyed  by  natural  selection 

Just  as  natural  selection  may  develop  an  appear- 
ance which  harmonises  with  the  surroundings,  out  of 
the  material  provided  by  non-significant  colour,  the 
same  agency  may  lead  to  the  disappearance  of  the 
latter  when  it  impedes  the  success  of  an  animal  hi  the 
struggle  for  existence.  Thus  the  red  colour  of  blood 
has  disappeared  in  certain  transparent  fishes,  which 
are  thereby  concealed  from  their  enemies.  Among  the 
manifold  possible  variations  of  nature  is  that  of  a 
fish  with  colourless  blood,  which  can,  nevertheless, 
efficiently  perform  all  the  duties  of  this  fluid.  While 
such  a  variation  would  be  no  advantage  to  the  great 
majority  of  vertebrates,  it  would  be  very  beneficial  to 


THE  USES  OF  COLOUR  15 

a  fish  which  was  already  difficult  to  detect  on  the 
surface  of  the  ocean  on  account  of  its  transparency. 

II.  Significant  colours 

Colours  may  be  useful  in  many  ways,  and  are  there- 
fore always  liable  to  be  turned  to  account  in  one  direc- 
tion or  another.  They  may  be  of  direct  physiological 
value  to  the  organism,  or  may  assist  in  the  struggle 
for  existence  by  deluding  other  species,  or  by  aiding 
the  individuals  of  the  same  species,  or  they  may  be 
intimately  connected  with  courtship. 

1.  The  Direct  Physiological  Value  of  colour 

The  colour  of  chlorophyll,  which  causes  the  green 
appearance  of  vegetation,  must  be  intimately  con- 
nected with  the  important  changes  which  take  place 
in  this  substance  in  the  presence  of  light.  It  is  well 
known  that  under  these  circumstances  carbon  dioxide 
(popularly  called  '  carbonic  acid ')  can  be  split  up, 
and  its  carbon  made  to  unite  with  the  elements  of 
water,  forming  organic  substance.  Although  this 
process  has  been  much  studied  it  is  still  very  imper- 
fectly understood.  It  is  clear,  however,  that  the 
colour  of  chlorophyll,  involving  the  special  absorp- 
tion of  certain  light-waves,  has  some  direct  bearing 
upon  the  changes  which  occur. 

No  equally  clear  instance  has  been  proved  to  occur 
in  the  animal  kingdom,  except  in  those  few  forms 


16         THE  COLOURS  OF  ANIMALS 

which  resemble  plants  in  possessing  chlorophyll.  Dr. 
Hickson,  however,  believes  that  among  corals '  the  most 
widely  distributed  colours  will  eventually  be  proved  to 
be  allied  to  chlorophyll .  .  .  and  perform  a  very  simi- 
lar if  not  precisely  identical  physiological  function.' 
It  is  much  to  be  desired  that  this  interesting  sugges- 
tion, which  Dr.  Hickson  supports  by  many  arguments, 
may  be  thoroughly  tested  as  soon  as  possible.1 

In  the  very  common  association  of  coloured  sub- 
stances with  the  important  function  of  respiration,  it 
is  clear  that  the  colour  is  not  more  than  incidental ; 
while  the  fish  with  transparent  blood  shows  that 
colour  is  not  indispensable  for  the  due  performance  of 
the  function.  Pigment  is,  however,  of  direct  import- 
ance for  vision :  it  is  always  present  in  the  eyes  of 
animals,  except  in  the  case  of  albinos,  and  it  is  said 
that  even  they  possess  the  essential  visual  pigment 
associated  with  the  termination  of  the  optic  nerve 
(retinal  purple). 

The  difference  between  the  physiological  importance 
of  colour  in  animals  and  plants  is  well  shown  by  the 
fact  that  a  true  albino  variety  (not  merely  a  varie- 
gated example)  of  a  green  plant  could  not  live  for  any 
length  of  iime. 

There  are,  however,  certain  cases  among  animals 
in  which  it  is  extremely  probable  that  colour  is  of 
direct  physiological  value.  It  is  well  known  that 
dark  colours  readily  absorb  radiant  heat,  while  light 

1  A  Naturalist  in  North  Cekbes  (Hiokson,  1889),  pp.  149-51. 


THE  USES  OF  COLOUR  17 

colours  do  so  with  difficulty.  For  this  reason  black 
clothes  are  most  trying,  and  white  most  comfortable, 
in  the  hottest  weather.  Conversely,  a  dark  surface 
readily  parts  with  heat  by  radiation,  while  a  white 
surface  retains  heat  far  more  effectually. 

A  few  writers  had  suggested  that  these  principles 
may  explain  the  colours  of  certain  animals,  but  the 
question  was  first  fully  entered  upon  in  Lord  Wal- 
singham's  presidential  address  to  the  Yorkshire 
Naturalists'  Union  in  1885. 1  The  predominance  of 
dark  varieties  of  insects  and  white  varieties  of  birds 
and  mammals  in  northern  latitudes  is  connected  with 
these  facts.  '  Birds  and  animals  living  through  the 
winter  naturally  require  to  retain  in  their  bodies  a 
sufficient  amount  of  heat  to  enable  them  to  maintain 
their  existence,  with  unreduced  vitality,  against  the 
severities  of  the  climate.  Insects,  on  the  contrary, 
require  rapidly  to  take  advantage  of  transient  gleams 
of  sunshine  during  the  short  summer  season,  and 
may  be  content  to  sink  into  a  dormant  condition  so 
soon  as  they  have  secured  the  reproduction  of  their 
species ;  only  to  be  revived  in  some  instances  by  a 
return  of  exceptionally  favourable  conditions.' 

It  would  be  fatal  for  the  temperature  of  one  of  the 
higher  vertebrates "  to  sink  a  few  degrees  below  the 
normal,  except  in  the  case  of  certain  species,  such  as  the 
dormouse,  &c.,  which  have  the  power  of  hybernating 
in  a  dormant  condition;  such  animals  were  once 

1  See  Entomological  Transactions  of  the  Union  for  1885. 


18         THE  COLOURS  OF  ANIMALS 

called  'warm-blooded,'  but  are  now  more  correctly 
termed  '  homothermic,'  because  it  is  the  constancy  of 
the  temperature  which  is  so  important,  and  which 
must  be  maintained  whether  the  surrounding  medium 
be  colder  or  warmer  than  themselves.  Other  animals 
with  an  inconstant  temperature  are  now  correctly 
called  '  poikilothermic '  rather  than  '  cold-blooded.' 

Lord  Walsingham's  conclusions  appear  to  be  sup- 
ported by  the  fact  that  young  dark-coloured  cater- 
pillars, like  those  of  the  Emperor  Moth  (Saturnia 
carpini),  or  Tortoiseshell  Butterfly  (Vanessa  urticce), 
seek  the  light  side  of  a  glass  cylinder,  and  always 
change  their  position  when  the  cylinder  is  turned 
round.  The  question  needs  further  investigation, 
and  much  might  be  learnt  by  interposing  various 
screens  between  such  larvae  and  the  light,  thus  cutting 
off  different  sets  of  light-waves. 

The  most  important  support  to  the  hypothesis  is 
found  in  an  experiment  made  by  Lord  Walsingham, 
in  which  several  Lepidoptera  of  different  colours  were 
placed  on  a  surface  of  snow  exposed  to  bright  sun- 
shine ;  in  half  an  hour  the  snow  beneath  the  darker 
insects  showed  distinct  signs  of  melting,  but  no  effects 
were  seen  beneath  the  others.  The  differences  were 
further  brought  out  in  the  course  of  two  hours,  when 
the  darkest  insect  of  the  lot,  a  black  Geometer,  the 
Chimney-Sweeper  (Odezia  charophyllata) ,  '  had  de- 
cidedly won  the  downward  race  among  them.' 

It  is  therefore   certain  that  the    absorption  of 


THE  USES  OF  COLOUR  19 

radiant  heat  is  favoured  by  the  dark  colours  of 
northern  insects,  and  it  is  in  every  way  probable  that 
they  are  benefited  by  the  warmth  received  in  this  way. 
We  cannot,  however,  as  yet  assert  that  such  dark 
colours  are  not  also  advantageous  for  concealment  or 
some  other  purpose. 

The  white  appearance  of  Arctic  birds  and  mam- 
mals must  be  advantageous  for  concealment  in  a  region 
so  largely  covered  with  snow,  but  it  is  very  probable 
that  advantage  is  also  secured  by  checking  the  loss  of 
heat  through  radiation. 

Thus  Lord  Walsingham's  experiments  and  con- 
clusions seem  to  prove  that  colours  are  sometimes 
of  direct  physiological  value  to  animals,  although  a 
great  deal  more  work  must  be  done  before  we  can 
safely  estimate  the  proportion  which  this  advantage 
bears  to  others  also  conferred  by  the  same  colours 
(see  also  pages  92-104). 


2.  Protective  and  Aggressive  Resemblance 

By  far  the  most  widespread  use  of  colour  is  to 
assist  an  animal  in  escaping  from  its  enemies  or  in 
capturing  its  prey  ;  the  former  is  Protective,  the  latter 
Aggressive.  It  is  probable  that  these  were  the  first  uses 
to  which  non-significant  colours  were  put.  The  re- 
semblances are  of  various  kinds ;  the  commonest  cases 
are  those  of  simple  concealment.  The  animal  passes 
undetected  by  resembling  some  common  object  which 


20  THE  COLOUES  OF  ANIMALS 

is  of  no  interest  to  its  enemies  or  prey  respectively, 
or  by  harmonising  with  the  general  effect  of  its  sur- 
roundings ;  the  former  is  Special,  the  latter  General 
Resemblance,  and  both  may  be  Protective  or  Aggressive. 
Among  the  most  interesting  Special  Aggressive  Resem- 
blances are  the  cases  of  Alluring  Colouring,  in  which  the 
animal,  or  some  part  of  it,  resembles  an  object  which 
is  attractive  to  its  prey. 

3.  Protective  and  Aggressive  Mimicry 

Mimicry  is  in  reality  a  very  important  section  of 
Special  Resemblance.  The  animal  gains  advantage  by 
a  superficial  resemblance  to  some  other,  and  generally 
very  different,  species  which  is  well  known  and  dreaded 
because  of  some  unpleasant  quality,  such  as  a  sting  or 
an  offensive  taste  or  smell,  &c.,  or  it  may  even  be  pro- 
tected from  the  animal  it  resembles :  this  is  Protective 
Mimicry.  When,  however,  the  animal  resembles  another 
so  as  to  be  able  to  injure  the  latter  or  some  other  form 
which  accompanies  it  or  is  not  afraid  of  it,  the  Mimicry 
is  Aggressive.  Although,  strictly  speaking,  Mimicry 
should  fall  under  the  last  heading,  it  is  so  important 
and  so  different  from  the  other  examples  of  Special 
Resemblance  that  it  is  more  convenient  to  consider  it 
separately.  In  the  complete  classification  at  the  end  of 
the  book  it  will  be  shown  in  its  true  position. 


THE  USES  OF  COLOUR  21 

4.  Warning  colours 

When  an  animal  possesses  an  unpleasant  attribute, 
it  is  often  to  its  advantage  to  advertise  the  fact  as 
publicly  as  possible.  In  this  way  it  escapes  a  great 
deal  of  experimental  '  tasting.'  The  conspicuous 
patterns  and  strongly  contrasted  colours  which  serve 
as  the  signal  of  danger  or  inedibility  are  known  as 
Warning  Colours.  In  other  cases  such  colours  or 
markings  enable  individuals  of  the  same  species  easily 
to  follow  those  in  front  to  a  place  of  safety,  or  assist 
them  in  keeping  together  when  safety  depends  upon 
numbers. 

It  is  these  Warning  Colours  which  are  nearly 
always  the  objects  of  Protective  Mimicry,  and  it  will 
therefore  be  convenient  to  describe  the  former  before 
the  latter. 

5.  Colours  produced  by  Courtship 

Finally,  in  the  highest  animals,  the  vertebrata  and 
many  of  the  most  specialised  invertebrate  groups,  we 
have  some  evidence  for  the  existence  of  an  aesthetic 
sense.  Darwin  believed  that  this  sense  was  brought 
into  play  in  courtship,  and  that  colours  and  patterns 
have  been  gradually  modified  by  the  preference  of  the 
females  for  the  most  beautiful  males ;  he  believed  that 
such  Sexual  Selection  accounts  for  many  of  the  most 
beautiful  features  possessed  by  animals,  viz.  those 
which  are  especially  displayed  during  courtship. 


22          THE  COLOURS  OF  ANIMALS 

Although  this  hypothesis  has  been  rejected  by  A.  B. 
Wallace,  I  shall  endeavour  to  support  it  by  some 
striking  observations  of  recent  date,  and  by  as  far  as 
possible  answering  the  objections  which  have  been 
raised,  and  the  hypotheses  which  have  been  believed 
to  account  for  the  same  facts. 

Display  in  courtship  is  probably  the  most  recently 
developed  of  all  the  various  uses  of  colour  among 
animals,  and  as  such,  its  consideration  is  best  deferred 
until  all  the  others  have  been  described. 

It  must  not  be  supposed  that  the  colours  of  each 
animal  will  be  found  to  possess  but  a  single  use. 
Thus  Protective  EesemUances  are  often  supplemented 
by  Warning  Colours  or  attitudes,  which  give  the 
animal  an  extra  chance  of  escape  after  its  first  line  of 
defence  has  been  broken  through.  It  is  also  the 
general  rule  for  the  colours  displayed  in  courtship  to 
be  hidden  beneath  protective  tints  when  the  animal 
is  at  rest. 

The  colours  of  animals  may  be  recapitulated  as 
follows : 

I.  NON-SIGNIFICANT  COLOURS. 

II.  SIGNIFICANT  COLOURS. 

1.  Colours  of  Direct  Physiological  Value. 

2.  Protective  and  Aggressive  Resemblance. 
8.  Protective  and  Aggressive  Mimicry. 

4.  Warning  Colours. 

6.  Colours  displayed  in  Courtship. 


THE  USES  OF  COLOUR  23 

The  rest  of  this  volume  will  be  occupied  with  the 
further  consideration  of  the  last  four  classes  of  colours. 
It  will  be  remembered  that  the  third  class  is  but  a 
special  example  of  the  second,  which  it  is  convenient 
to  treat  separately,  and  to  defer  until  after  the  fourth 
class  has  been  considered. 


24          THE  COLQUES  OF  ANIMALS 


CHAPTER  m 

PROTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA 

THE  first  and  most  important  use  of  colour  is  to 
enable  an  animal  to  conceal  itself  from  its  enemies 
or  to  approach  its  prey  unseen.1 

Special  and  General  Resemblances 

These  results  may  be  achieved  in  one  of  two  ways : 
either  the  animal  may  more  or  less  exactly  resemble 
some  object  which  is  of  no  interest  to  its  enemies,  or 
it  may  harmonise  with  the  general  artistic  effect  of 
its  surroundings,  so  that  it  does  not  attract  attention. 
We  may  therefore  distinguish  Special  Resemblance,  in 
which  the  appearance  of  a  particular  object  is  copied 
in  shape  and  outline  as  well  as  in  colour,  and  General 
Resemblance,  in  which  the  general  effects  of  surround- 
ing colours  are  reproduced. 

In  the  latter  case  it  is  often  difficult  to  believe, 


1  This  was  thoroughly  appreciated  by  Erasmus  Darwin,  who 
says :  '  The  colours  of  many  animals  seem  adapted  to  their  purposes 
of  concealing  themselves,  either  to  avoid  danger  or  to  spring  upon 
their  prey.' — Zoonomia,  1794,  vol.  i.  p.  509. 


PKOTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA     25 

when  we  look  at  the  animal  by  itself,  that  the  pro- 
tection is  effective  and  real.  We  cannot  appreciate 
the  meaning  of  the  colours  of  many  animals  apart 
from  their  surroundings,  because  we  do  not  compre- 
hend the  complicated  artistic  effect  of  the  latter.  A 
caterpillar  in  the  midst  of  green  leaves  may  have 
many  brilliant  tints  upon  it,  and  yet  may  be  all  the 
better  concealed  because  of  their  presence ;  the  ap- 
pearance of  the  foliage  is  really  less  simple  than  we 
imagine,  for  changes  are  wrought  by  varied  lights 
and  shadows  playing  upon  colours  which  are  in  them- 
selves far  from  uniform. 

Francis  Galton  noticed  this  fact  with  regard  to  the 
higher  animals  in  1851.  '  Snakes  and  lizards  are  the 
most  brilliant  of  animals  ;  bat  ah1  these,  if  viewed  at  a 
distance,  or  with  an  eye  whose  focus  is  adjusted,  not 
exactly  at  the  animal  itself,  but  to  an  object  more  or 
less  distant  than  it,  become  apparently  of  one  hue 
and  lose  all  their  gaudiness.  No  more  conspicuous 
animal  can  well  be  conceived,  according  to  common 
idea,  than  a  zebra ;  but  on  a  bright  starlight  night  the 
breathing  of  one  may  be  heard  close  by  you,  and  yet 
you  will  be  positively  unable  to  see  the  animal.  If 
the  black  stripes  were  more  numerous  he  would  be 
seen  as  a  black  mass ;  if  the  white,  as  a  white  one ; 
but  their  proportion  is  such  as  exactly  to  match  the 
pale  tint  which  arid  ground  possesses  when  seen  by 
moonlight.' l 

1  Galton's  South  Africa,  p.  187  (Minerva  Library). 


26         THE  COLOURS  OF  ANIMALS 

We  shall  see  that  it  is  common  for  an  insect  to  be 
protected  by  Special  Resemblance  at  one  time  of  its 
life,  and  by  General  Resemblance  at  another,  or  to 
be  concealed  at  different  periods  of  its  life  by  different 
kinds  of  Special  or  General  Resemblance  respectively. 

Each  of  these  forms  of  Resemblance  may  be 
Protective  or  Aggressive  according  as  they  are  made 
use  of  to  defend  from  attack  or  to  assist  in  capture. 
We  shall  also  see  that  Protective  and  Aggressive  Re 
semblances  may  be  either  Constant  or  Variable ;  in 
the  latter  case,  the  appearance  is  capable  of  adjust- 
ment in  order  to  correspond  with  changes  in  the  en- 
vironment. This,  the  highest  form  of  Resemblance, 
will  be  deferred  until  the  examples  of  the  other  form 
have  been  considered. 


The  Larvse  of  Geometrse  as  examples  of  Special 
Protective  Resemblance 

There  is  no  better  instance  of  Special  Protective 
Resemblance  than  that  afforded  by  the  larvae  of 
Geometra,  *  stick  caterpillars '  or  '  loopers,'  as  they 
are  often  called.  These  caterpillars  are  extremely 
common,  and  between  two  and  three  hundred  species 
are  found  in  this  country ;  but  the  great  majority  are 
rarely  seen  because  of  their  perfect  resemblance  to 
the  twigs  of  the  plants  upon  which  they  feed.  They 
possess  only  two  pairs  of  claspers,  or  legs  which  are 
peculiar  to  the  caterpillar  stage,  while  in  nearly  all 


PEOTECTIVE  KESEMBLANCES  IN  LEPIDOPTEEA     27 

other  caterpillars  there  are  five  pairs.  These  claspers 
are  placed  at  the  hind  end  of  the  body,  which  is 
long,  thin,  and  cylindrical,  and  stands  out  like  a 
side  twig  at  an  acute  angle  with  the  stem  to  which 
the  claspers  are  tightly  fixed.  The  body  also  often 
possesses  little  humps  which  resemble  buds  or  irregu- 
larities of  the  bark.  The  caterpillar  sits  motionless 


FIG.  1.—  The  larva  of  Swallow-tail  Moth 
(Ourapteryx  tambucaria)  ;  last  stage  ; 
natural  size. 


FIG.  2.—  Twig  of  currant  ;  the  general 
appearance  much  like  that  of  fig.  1. 


for  hours  together,  and  the  only  alteration  of  the 
attitude  is  brought  about  by  feeding,  which  generally 
takes  place  in  the  evening  or  at  night.  The  general 
appearance  of  one  of  these  larvse  and  its  resemblance 
to  a  twig  is  shown  in  figs.  1  and  2,  for  which  I  am 
indebted  to  the  kindness  of  Mr.  Alfred  Sich. 

The  strain  on  the  body  during  these  long  periods 


28 


THE  COLOUES  OF  ANIMALS 


of  absolute  stillness  would  be  far  too  great  to  be 
borne  did  not  the  caterpillar  spin  a  thread  of  silk, 
•which  is  attached  at  one  end  to  the  stem,  while  the 
other  end  remains  fixed  to  the  head  of  the  animal. 
How  great  the  strain  would  be  without  such  a  support 
may  be  well  understood  by  any  one  who  has  tried  to 
hold  out  the  arm  straight  at  right  angles  to  the  body 
for  five  minutes.  There  is  considerable  tension  upon 
the  thread  of  silk,  so  that,  if  it  be 
cut,  the  larva  falls  back  with  a  jerk, 
making  a  more  obtuse  angle  with 
the  stem  ;  and  it  then  tries  to  remain 
rigid  in  the  new  position  :  this  is  im- 
possible because  of  the  strain,  and 
after  again  falling  backwards  once  or 
twice,  and  making  one  or  two  more 
attempts  to  keep  firm  and  motionless, 
it  is  obliged  to  give  up  the  twig-like 
position  while  it  fixes  a  new  sup- 
porting thread.  In  some  cases  the 
caterpillar  gains  support  by  holding 
a  leaf  or  twig  with  one  of  its  three 
pairs  of  true  legs,  or  legs  which  will  persist  in  the 
perfect  insect  (see  fig.  3 ;  also  figs.  40  and  41,  page  152). 
These  pairs  of  legs  are  placed  one  on  each  of  the 
body-rings  behind  the  head. 

It  is  very  interesting  to  notice  how  the  head  of 
these  caterpillars  is  modified  from  the  usual  shape 
into  one  which  suggests  the  end  of  a  twig.  It  is  very 


FIG.  3.— The  larva  of 
Peppered  Moth  (Am- 
phidasii  bttularia)  • 
last  stage;  natural 


PROTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA      29 


common  for  the  crown  to  be  deeply  notched,  thus 
producing  two  humps  which  make  a  very  natural  end 
to  the  apparent  twig.  In  the  caterpillar  of  the  Small 
Emerald  Moth  (Hemithea  thymiaria)  there  are  two 
additional  humps  on  the  body-ring  (prothorax)  behind 
the  head,  and  the  latter  is  bent  forwards  and  inwards, 
so  that  the  end  of  the  caterpillar  is  made  up  of  four 
blunt  projections,  forming  perhaps 
the  most  suggestive  of  all  the  resem- 
blances to  the  end  of  a  twig. 

In  the  larva  of  the  Early  Thorn 
Moth  (Selenia  illunaria)  the  head 
and  first  two  body-rings  are  bent 
backwards  at  right  angles  to  the  rest 
of  the  body.  The  supporting  thread 
of  silk  passes  between  the  third  pair 
of  true  legs,  which  a,re  borne  by  a 
high  ridge  projecting  from  the  angle. 
The  ridge  continues  the  line  of  the 
body,  and  is  coloured  like  it,  while 
the  head  and  first  rings  are  of  a 
different  colour.  The  whole  effect  is  exceedingly  un- 
caterpillar-like,  and  very  suggestive  of  some  eccentric 
vegetable  growth  (see  fig.  4). 

In  order  that  the  resemblance  may  be  complete,  it 
is  essential  that  the  caterpillar  should  appear  to  grow 
out  of  the  branch  in  a  natural  manner.  The  two 
pairs  of  claspers  assist  in  producing  this  effect,  for 
they  partially  encircle  the  branch,  and  appear  to  be 
3 


FIG.  4.— The  larva  of 
Early  Thorn  Moth 
(Selenia  illunaria)  ; 
adult ;  natural  size. 


30 


THE  COLOURS  OF  ANIMALS 


continuous  with  it  (see  fig.  7,  page  31).  Between  the 
two  pairs  there  is  necessarily  a  furrow,  where  the  body 
of  the  larva  lies  along  the  cylindrical  branch.  This 
furrow,  which,  if  apparent,  would  greatly  interfere  with 
the  resemblance,  is  rendered  inconspicuous  in  the  fol- 
lowing manner.  The  under  side  of  the  caterpillar  is 
somewhat  flattened,  so  that  it  is  in  contact  with  a 
small  part  of  the  circumference  of  the  branch,  and 
the  furrow  on  each  side  is  partially  filled  up,  at  any 


rate  in  certain  species,  by  a  number  of  fleshy  tubercles. 
The  shadow  which  would  betray  the  furrow  is  also 
neutralised  by  the  light  colour  of  the  tubercles.  The 
effect  will  be  clear  on  comparing  a,  b,  and  c  in  fig.  5  : 
a  is  a  section  of  a  branch  just  below  the  point  where 
a  lateral  twig  comes  off ;  6  a  diagrammatic  section  of 
a  branch  and  the  caterpillar's  body ;  c  the  same  with 
the  addition  of  the  tubercles,  which  render  the  outline 
more  like  that  of  a. 

I  will  illustrate  the  extraordinary  degree  of  resem- 


PKOTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA      31 

blance  attained  in  Geometra,  by  a  description  of  the 
larva  of  one  of  our  most  abundant  species — the  Brim- 
stone Moth  (Rumia  cratcegata).  The  appearance  of  the 
larva  when  seated  among  the  twigs  of  its  commonest 
food -plant — hawthorn — is  shown  in  fig.  6.  It  will  be 
observed  that  some  of  the  twigs  are  slightly  bent  in 
the  middle,  and  that  a  projection  is  placed  on  the 
angle;  these  appearances  are  exactly  reproduced  in 


Fio.    6.— The    larva    of  FIG.  7.-The  hind  part  of  the  larva  of  Brimstone 

Brimstone  Moth    (Ru-  Moth  (Rumia  cratoegata),  seen  from  right 

mia    craiaegatd) ;    last  side,  showing  junction  with  branch  •  adult 
stage ;  natural  size. 


the  larva.  The  hind  part  of  the  larva  is  represented 
in  fig.  7  (magnified  4-5  diameters),  showing  the 
claspers  and  the  fleshy  projections  which  occupy  the 
furrow  between  the  larva  and  the  stem. 

The  harmony  of  colour  is  quite  as  perfect  as  the 
resemblance  of  shape.  The  smaller  branches  of  the 
hawthorn  are  partially  covered  by  a  thin  superficial 
layer  of  a  bluish-grey  colour  (the  cuticle),  while  the 


32          THE  COLOURS  OF  ANIMALS 

deeper  layers  beneath  are  brown  or  green,  or  mixed 
brown  and  green ;  these  tints  become  visible  over  a 
large  part  of  the  surface,  owing  to  the  breaking 
away  of  the  thin  layer.  Hence  the  colour  of  the 
branches  is  brown  or  green,  mottled  with  grey,  and 
not  only  are  these  the  exact  tints  of  the  larva, 
but  the  way  in  which  the  colours  are  blended  is 
precisely  similar  hi  the  annual  and  the  plant.  The 
marvellous  fidelity  with  which  the  details  are  thus 
reproduced,  probably  implies  that  the  relation  between 
the  larva  and  this  species  of  food-plant  is  extremely 
ancient.  It  will  be  shown  below  that  this  caterpillar 
can  also  adjust  its  colour  to  that  of  its  individual 
surroundings,  so  that  it  would  become  greenish  if  it 
passed  its  life  among  young  green  shoots,  and  brown 
if  it  lived  upon  the  older  twigs.  It  is  altogether  one 
of  the  most  perfectly  concealed  forms  in  existence. 

When,  however,  such  'stick  caterpillars'  are 
young,  they  do  not  sit  upon  the  branches,  but  upon 
the  leaves  of  their  food-plant,  and  the  twig-like 
attitude  would  then  be  inappropriate,  for  we  do  not 
see  twigs  projecting  from  leaves.  In  some  cases  the 
caterpillars  are  green  (e.g.  Ephyra  omicronaria) ,  and 
so  possess  a  general  harmony  with  the  colour  of  the 
surface  behind  them;  but  in  other  cases  they  are 
brown,  and  then  the  attitude  is  often  modified  into 
a  different  form  of  Special  Resemblance.  The 
caterpillar  twists  itself  into  a  very  irregular  spiral 
(e.g.  Ephyra  pendularia,  &c.),  or  into  an  exceedingly 


PROTECTIVE  RESEMBLANCES  IN  LEPEDOPTERA      33 

angular  zigzag  (e.g.  Selenia  illunaria;  see  fig.  8),  thus 
resembling  a  dead  and  crumpled  piece  of  leaf,  or  the 
spiral  leaf-case  made  by  other  insects,  or  the  excre- 
ment of  birds  or  snails.  The  caterpillar  of  Selenia 
illunaria  has  a  very  similar  structure  and  colouring 
at  the  times  when  it  resembles  such  very  different 
objects  as  a  twig  and  the  excrement  of  a  bird,  the 
whole  difference  being  made  by  a  modification  of  atti- 
tude alone  (compare  figs.  4  and  8).  I  have  seen  the 
larva  of  the  Brimstone  Moth  twisted  into  a  spiral, 
resting  motionless  close  to  the 
notch  which  it  had  eaten  out  of 
a  leaf ;  in  this  position  it  forcibly 


suggested   the  appearance  of  a     *«».  8--The  you 

Early  Thorn  (• 

small  piece  of  leaf  which  had 

been  accidentally  torn,  and  had 

turned  brown  and  curled  up,  remaining  attached  to 

the  uninjured  part  of  the  leaf  by  one  end. 

We  may  well  suppose  that  the  acquisition  of  a 
form  and  attitude  which  lend  themselves  so  readily  to 
the  purposes  of  concealment,  was  very  advantageous 
to  the  ancestral  Geometra,  and  enabled  them  to  spread 
over  the  vegetable  world,  dividing  into  an  immense 
number  of  species,  and  ousting  many  larvae  with  less 
perfect  methods  of  concealment.  In  their  widening 
range  certain  Geometrce  have  thus  come  to  feed  upon 
low-growing  plants  which  are  altogether  without  twigs 
or  branches.  The  attitude  is  then  modified,  and  sug- 
gests some  object  which  might  be  expected  to  occur 


34 


THE  COLOURS  OF  ANIMATE 


upon  the  plant.  Thus  the  caterpillar  of  the  Straw 
Belle  (Aspilates  gilvaria),  feeding  upon  such  plants  as 
yarrow  and  plantain,  coils  up  the  anterior  part  of  its 
body  into  a  flat  spiral,  with  the  head  in  the  centre. 
Hence  the  attitude  and  the  whitish  colour  of  the  larva 
produce  a  very  considerable  resemblance  to  a  small 
bleached  and  empty  snail-shell,  which 
would  be  of  no  interest  to  any  insect- 
eater.  If  the  colour  of  the  caterpillar 
were  darker  it  might  be  mistaken  for 
a  living  snail,  and  it  is  doubtful  how  far 
such  a  resemblance  would  be  to  its  ad- 
vantage, in  the  case  of  birds. 

Another  larva,  that  of  the  Large 
Emerald  Moth  (Geometra  papilionaria), 
feeding  upon  catkin -bearing  trees,  birch 
and  nut,  resembles  the  catkins  rather 
than  the  twigs  (see  fig.  9).  It  is  short 
and  stout,  and  the  manner  in  which  the 
body-rings  succeed  each  other  forcibly 
suggests  the  overlapping  scales  of  a  cat- 
kin. Some  of  the  larva?  are  green  and 
some  brown,  like  catkins  of  different  colours. 


FIG.  9.  -  The 
larva  of  Large 
Emerald  Moth 
(Geometra 
papilionaria); 
a  green  va- 
riety ;  last 
stage;  natural 


Protective  Resemblance  to  bark  and  lichen  in 
Lepidoptera 

Certain  caterpillars  belonging  to  other  groups  are 
concealed  by  their  resemblance  to  the  bark  of  tolerably 


PROTECTIVE  RESEMBLANCES   IN   LEPIDOPTERA      35 

thick  branches.  They  lie  flattened  and  closely  pressed 
against  the  bark ;  while  the  furrow  which  would  lead 
to  their  detection  is  partially  filled  up,  and  the 
shadow  neutralised,  by  a  row  of  fleshy  protuberances 
in  the  caterpillars  of  the  Eed  and  Crimson  Under- 
wing  Moths  (Catocalida ;  see  figs.  38  and  39,  page 
151),  and  by  hairs  in  the  larva  of  the  December  Moth 
(Pcecilocampa  populi).  This  interpretation  was  first 
offered  by  Meldola,  and  it  is  strongly  supported  by 
the  previously  mentioned  fact  that  similar  protuber- 
ances occur  in  Geometrce,  and  are  strictly  confined  to 
the  comparatively  short  line  of  contact  between  the 
larva  and  the  branch.  The  lichens  on  the  bark  are 
very  commonly  resembled  rather  than  the  bark  itself. 
This  is  the  case  with  the  last-named  larva.  The 
caterpillar,  chrysalis,  and  moth  of  the  Black  Arches 
(Psilura  monacha)  are  beautifully  protected  in  this 
way.  The  black  pupa  is  fixed  in  a  chink  in  the  bark 
by  a  few  inconspicuous  threads ;  its  dark  colour  har- 
monises with  the  shadow  in  the  chink,  while  the  long 
tufts  of  greyish  hair  project  and  exactly  resemble  the 
appearance  of  lichen.  Both  larva  and  moth  are 
coloured  so  as  to  resemble  common  appearances  pre- 
sented by  lichens,  and  both  habitually  rest  on  lichen- 
covered  bark.  A  lichen-feeding  Geometer  (Cleora 
lichenaria)  is  wonderfully  protected  in  the  same 
manner ;  the  larva  often  twists  itself  among  the 
irregularities  of  the  lichen,  so  that  it  is  completely 


36 


THE  COLOURS  OF  ANIMALS 


invisible.    The  moth  is  also  similarly  concealed,  and 
rests  on  tree-trunks. 


A  caterpillar  which  makes  its  surroundings 
resemble  itself 

In  all  the  examples  hitherto  described,  and  count- 
less others,  the  insect  is  defended  by  resembling  its 
surroundings ;  the  very  interesting  caterpillar  of 

a  South  American 
butterfly.  (Anaea 
sp.  ?),  described  by 
Wilhelm  Muller, 
acts  differently  and 
makes  its  surround- 
ings resemble  itself. 
It  gnaws  the  leaf  in 
such  a  manner  as  to 
leave  a  number  of 
rough  models  of  it- 
self attached  to  the 
mid-rib,  and  then  sits  down  beside  them.  The  cater- 
pillar is  green  above  and  dark  beneath,  although 
the  former  colour  interrupts  the  latter  at  certain 
points  and  comes  into  contact  with  the  mid-rib  on 
which  the  insect  is  resting.  The  dark  colour  is  not 
distinguishable  from  the  deep  shadow  behind  the 
leaf,  and  therefore  the  appearance  is  that  of  an 
elongated  patch  of  green  connected  with  the  mid- 


FIG.  10. — The  larva  of  Anaea  sp.  t  on  the  mid-rib 
of  a  leaf  on  which  are  many  pieces  of  leaf  of 
the  general  appearance  of  the  larva;  third 
stage  ;  natural  size  ;  after  Wilhelm  Muller. 


PROTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA      37 

rib  by  two  narrow  stalks.  The  larva,  in  eating, 
leaves  several  pieces  of  leaf  attached  to  the  mid-rib  by 
one  or  two  stalks,  which,  therefore,  present  a  very 
similar  appearance  to  that  of  the  larva  itself.  The 
concealment  which  is  thus  effected  is  sufficiently 
indicated  in  fig.  10. 


An  appearance  of  leaf-like  flatness  conveyed  by 
arrangement  of  colour 

Another  very  interesting  example,  in  which  the 
effect  of  shadow  is  gained  by  arrangement  of  colour, 
is  afforded  by  the  chrysalis  of  the  Purple  Emperor 
Butterfly  (Apatura  iris).  The  large  green  pupa  re- 
sembles a  leaf  in  the  most  perfect  manner,  mid-rib 
and  oblique  veining  being  represented.  I  showed  a 
small  twig  of  sallow,  to  which  a  pupa  was  suspended, 
to  several  friends,  but  it  was  almost  invariably  over- 
looked ;  even  when  it  was  pointed  out,  the  observer 
frequently  failed  to  see  any  difference  between  it  and 
a  sallow  leaf.  The  most  extraordinary  thing  about 
this  resemblance  is  the  impression  of  leaf-like  flatness 
conveyed  by  a  chrysalis,  which  is  in  reality  very  far 
from  flat.  In  its  thickest  part  the  pupa  is  8'5  mm. 
across,  and  it  is  in  all  parts  very  many  times  thicker 
than  a  leaf.  The  dorsal  side  of  the  pupa  forms  a 
very  thin  sharp  ridge  for  part  of  its  length,  but  the 
slope  is  much  more  pronounced  in  other  parts  and 
along  the  whole  ventral  side.  But  exactly  in  these 


38         THE  COLOURS  OF  ANIMALS 

places,  where  the  obvious  thickness  would  destroy  the 
resemblance  to  a  leaf,  the  whole  effect  of  the  round- 
ness is  neutralised  by  increased  lightness,  so  disposed 
as  just  to  compensate  for  the  shadow  by  which  alone 
we  judge  of  the  roundness  of  small  objects.  The 
degree  of  whiteness  is  produced  by  the  relative  abun- 
dance of  white  dots  and  a  fine  white  marbling  of  the 
surface,  which  is  everywhere  present  mingled  with  the 
green.  The  effect  is,  in  fact,  produced  by  a  process 
exactly  analogous  to  stippling.  The  degree  of  lightness 
produced  in  this  way  exactly  corresponds  to  the  angle 
of  the  slope,  which,  of  course,  determines  the  depth 
of  the  shadow.  By  this  beautiful  and  simple  method 
the  pupa  appears  to  be  as  flat  as  a  leaf  which  is  only 
a  small  fraction  of  1  mm.  in  thickness. 

Although  the  effect  which  I  have  just  described 
could  not  have  been  surpassed  by  the  efforts  of  an 
artist,  it  is  precisely  the  result  which  can  be  most 
readily  explained  by  the  unaided  operation  of  natural 
selection.  The  minute  white  markings  are  present. 
over  the  whole  surface,  and  their  number  and  size 
must  be  subject  to  continual  variation ;  in  fact,  it  is 
quite  certain  that  no  two  individuals  are  alike  in  these 
respects.  The  increased  protection  afforded  by  their 
more  appropriate  distribution  in  certain  individuals 
would  clearly  lead  to  the  survival  of  the  latter,  while 
the  same  process  continued  in  each  generation  would 
lead  to  the  elaborate  and  beautiful  form  of  adaptation 
which  is  now  witnessed  in  this  species. 


PROTECTIVE  RESEMBLANCES  IN  LEPIDOFTERA      39 

An  analogous  effect  is  produced  by  the  larva  of  a 
Saw-fly  (a  plant-eating  Hymenopterous  insect),  which 
rests  stretched  along  the  edge  of  a  leaf.  In  this  posi- 
tion the  larva  (Nematus  curtispina)  would  be  detected 
if  it  covered  the  notched  edge  of  the  leaf ;  it  has,  how- 
ever, the  habit  of  resting  along  the  curved  edge  of  the 
gap  made  by  its  own  exertions.  From  the  side  its 
green  ground  colour  is  alone  apparent,  and  it  is  very 
difficult  to  detect.  When,  however,  the  leaf  is  looked 
at  edgeways,  it  would  seem  that  the  larva  must  be  con- 
spicuous, because  its  thickness  is  much  greater  than 
that  of  a  leaf.  From  this  point  of  view  the  back  of 
the  larva  is,  of  course,  seen;  along 
the  middle  line  the  tubular  heart  is 


more  distinct  than  usual  because  of   FIG.  11.— The  larva  of 

Nematus     curtispina ; 

the  transparent  skin.  The  green  must  stage ;  natural 
blood  within  makes  the  heart  appear 
as  a  fine  dark  line  against  a  white  border  on  each 
side,  which  is  entirely  due  to  an  accumulation  of  fat 
beneath  the  skin.  The  white  band  with  the  fine  dark 
line  down  its  middle  produces  the  effect  of  the  edge  of 
the  leaf,  while  the  rest  of  the  body  on  each  side  is 
green,  shaded  with  dark  pigment  so  as  to  appear  much 
flatter  than  it  really  is.  The  appearance  of  the  larva 
is  shown  in  fig.  11. 

The  case  is  also  of  special  interest,  because  the 
colouring  is  chiefly  derived  from  internal  tissues  or 
organs  showing  through  a  transparent  skin.  The 
ground  colour  is  due  to  the  green  fluids  of  the  body 


40  THE  COLOURS  OF  ANIMALS 

and  the  green  contents  of  the  alimentary  canal.  The 
dark  shading  is  the  only  part  of  the  appearance  caused 
in  the  usual  way  by  superficially  placed  pigment. 
Nearly  all  the  colours  of  this  animal  are  non- 
significant in  many  other  insects. 


Eeply  to  objection  that  methods  of  concealment 
would  certainly  be  detected 

It  has  been  sometimes  objected  that  these  methods 
of  concealment  cannot  be  intended  as  a  means  of 
defence,  because  insect-eating  animals  would  be 
sharp-sighted  enough  to  penetrate  the  disguise.  Of 
course,  the  progressive  improvement  in  the  means 
of  concealment  has  been  attended  by  a  corresponding 
increase  in  the  keenness  of  foes,  so  that  no  species 
can  wholly  escape.  But  so  long  as  a  well-concealed 
form  remains  motionless,  it  is  easy  to  prove  by 
experiment  that  enemies  are  often  unable  to  recog- 
nise it.  Thus  I  have  found  that  the  insect-eating, 
wood-haunting  Green  Lizard  (Lacerta  viridis)  will 
generally  fail  to  detect  a  '  stick  caterpillar '  in  its 
position  of  rest,  although  it  is  seized  and  greedily 
devoured  directly  it  moves.  The  marvellous  resem- 
blance of  Cleora  lichenaria  (see  p.  35)  even  deceived 
one  of  these  lizards  after  the  larva  had  moved  more 
than  once.  The  instant  the  caterpillar  became  rigid 
the  lizard  appeared  puzzled,  and  seemed  unable  to 
realise  that  the  apparent  piece  of  lichen  was  good  to 


PROTECTIVE  RESEMBLANCES   IN  LEPIDOPTERA      41 

eat.  After  a  few  moments,  however,  the  lizard  was 
satisfied,  and  ate  the  caterpillar  with  the  keenest 
relish. 

Furthermore,  the  fact  that  all  well-concealed 
forms  are  good  for  food,  and  are  eagerly  chased  and 
devoured  by  insectivorous  animals,  while  unpalatable 
forms  are  conspicuously  coloured,  points  strongly 
towards  the  conclusion  that  the  object  of  concealment 
is  defence  from  enemies. 


42  THE  COLOUKS  OF  ANIMALS 


CHAPTER  IV 

PROTECTIVE  RESEMBLANCES  IN  LEPIDOPTERA 
(continued),  DIMORPHISM,  ETC. 

General  Protective  Resemblance  and  changes  of  colour 
corresponding  to  changes  in  the  surroundings 

ALL  the  examples  hitherto  described  illustrate  Special 
Protective  Resemblance.  A  good  instance  of  General 
Resemblance  is  afforded  by  the  large  and  common 
caterpillar  of  the  Privet  Hawk  Moth  (Sphinx  ligustri). 
Although  the  caterpillar  looks  so  conspicuous,  it 
harmonises  very  well  with  its  food-plant,  and  is  some- 
times difficult  to  find.  The  purple  stripes  increase 
the  protection  by  breaking  up  the  large  green  surface 
of  the  caterpillar  into  smaller  areas.  This  cater- 
pillar also  affords  a  good  example  of  a  rapid  change  of 
colour  corresponding  to  a  change  of  environment. 
When  full  grown  it  descends  to  the  ground  and 
hurries  about  in  search  of  a  spot  to  bury  in,  and, 
being  very  large  and  bright  green,  it  would  be  ex- 
ceedingly conspicuous  against  the  brown  earth  if  it 
retained  the  usual  colour.  But  just  before  it  descends 
the  back  begins  to  turn  brown,  and  becomes  finally 


PEOTECTIVE  RESEMBLANCES— DIMORPHISM,  ETC.      43 

dark  brown,  so  that  the  caterpillar  harmonises  well 
with  the  colour  of  its  new  surroundings.  The  sig- 
nificance of  this  change  was  first  pointed  out  by 
Professor  Meldola.  Other  nearly  allied  caterpillars 
feeding  upon  trees,  such  as  willow  or  poplar,  which 
grow  in  damp  situations  where  the  ground  is  covered 
with  green  vegetation,  do  not  turn  brown  to  anything 
like  the  same  extent. 

A  very  interesting  instance  of  exactly  the  opposite 
change  at  a  corresponding  period  is  afforded  by  the 
caterpillar  of  the  August  Thorn  Moth  (Ennomos  angu- 
larid),  a  brown  '  stick  caterpillar,'  protected  by  a  very 
perfect  Special  Eesemblance  to  the  dark  twigs  of  the 
elm  on  which  it  feeds.  When  full-fed  it  constructs  a 
very  loose  cocoon  of  elm  leaves,  so  loose  and  open  that 
it  is  easily  seen  within,  and  its  brown  body  would  be 
conspicuous  against  the  background  of  green  leaves. 
But  at  the  same  time  the  dark  brown  colour  of  its 
surface  entirely  disappears,  and  the  animal  is  tinted 
by  its  green  blood,  which  is  seen  through  the  trans- 
parent skin ;  it  is  thus  well  concealed  by  General 
Resemblance  to  its  new  surroundings. 

Another  exceedingly  interesting  case  of  the  same 
kind  of  change  is  witnessed  in  the  caterpillar  of  the 
Miller  Moth  (Acronycta  leporina),  which  sits  motionless 
on  the  under  side  of  the  leaves  of  the  birch  and  alder, 
and  is  covered  with  very  long  beautiful  hair  which  is 
brilliantly  white,  and  bends  over  on  all  sides  so  as  to 
touch  the  leaf,  forming  a  wide  margin  round  the 


44  THE  COLOURS  OF   ANIMALS 

caterpillar.  Hence  all  we  can  see  is  an  oval  convex 
mass  of  a  substance  resembling  white  cotton  wool,  an 
appearance  very  suggestive  of  a  cocoon  (see  fig.  12). 
The  caterpillar's  body  is  almost  invisible  ;  but  on 
looking  carefully  we  can  just  make  out  a  dim  curved 
shape  beneath  the  white  covering,  just  as  a  caterpillar 
or  chrysalis  appears  through  the  walls  of  its  cocoon : 


PIG.  12. -The  larva  of  Miller  Moth  (Aero-       FIG.  13.  -Thelarva  of  Miller  Moth  (Aero- 
nyctaleporina),  at  rest  on  a  birch  leaf  ;  nycta  leporina),  wandering  about  on 

adult ;  natural  size.  bark  before  forming  cocoon ;  natural 

size. 

furthermore,  the  larva  is  very  short  and  thick,  and  thus 
resembles  the  contracted  state  of  a  caterpillar  before 
turning  to  a  chrysalis.  This  perfect  Special  Eesem- 
blance  is  kept  up  until  the  caterpillar  is  full-fed, 
when  it  wanders  over  the  bark  and  finally  burrows 
in  it.  But  a  cocoon  is  a  motionless  object,  and 
the  resemblance,  if  continued,  would  be  fatal,  for  it 
would  attract  attention.  But  as  soon  as  the  larva 


PEOTECTIVE  RESEMBLANCES— DIMOKPHISM,   ETC.      45 

is  mature,  the  hairs  become  black  and  the  body  of  a 
much  darker  tint,  and  the  animal  is  then  well  pro- 
tected by  General  Eesemblance  to  the  dark  surface 
over  which  it  moves  (see  fig.  13). 

Although  the  bark  of  large  birch  trees  is  chiefly 
white,  the  caterpillar  is,  upon  the  whole,  better  con- 
cealed by  becoming  dark-coloured.  It  lives  on  small 
birches  and  alders  with  dark  bark,  as  well  as  on 
large  birches,  and  in  the  latter  case  it  probably 
wanders  among  the  wide  dark  chinks  rather  than 
over  the  smooth  wide  expanses,  for  it  would  certainly 
burrow  in  the  former  rather  than  the  latter. 

Just  before  pupation  the  colours  of  caterpillars 
nearly  always  become  dull,  and  it  is  in  every  way 
probable  that  such  incidental  changes  have  been 
seized  upon  by  natural  selection,  and  have  been  ren- 
dered advantageous  to  the  species.  Such  alterations 
of  colour  are  entirely  different  from  those  which  will 
be  described  below,  in  which  an  animal  can  modify  its 
appearance  into  correspondence  with  its  individual 
surroundings.  The  larva  of  the  Privet  Hawk  Moth 
almost  invariably  wanders  over  the  earth  when  it 
has  come  down  from  its  food-plant ;  but  if  it  were  to 
descend  upon  turf,  the  brown  colour  would  still  be 
assumed,  although  green  would  conceal  it  more  effec- 
tually. The  change  to  brown  is,  however,  far  safer 
for  the  average  caterpillar,  and  is  beneficial  to  the 
species  on  the  whole,  although  it  must  lead  to  some  in- 
dividual failures.  In  the  far  higher  form  of  Variable 


46          THE  COLOURS  OF  ANIMALS 

Protective  Resemblance,  which  will  be  described  in 
Chapters  VII.,  VIII.,  and  IX.,  the  individual  can 
adjust  its  appearance  to  any  of  the  various  environ- 
ments it  is  h'kely  to  meet  with  in  nature. 

The    consideration    of    changes    in   colour    very 
naturally  leads  to  the  subject  of  Dimorphism. 


Dimorphism  in  Lepidopterous  larvae 

It  has  been  already  mentioned  that  the  caterpillars 
of  the  Large  Emerald  Moth  are  sometimes  green  and 
sometimes  brown.  The  same  is  true  of  many  larvae, 
and  in  some  of  the  Mocha  Moths  (Ephyrida)  the 
chrysalides  are  the  same  colour  as  the  larvae  from  which 
they  develop.  These  colours  have  nothing  to  do  with 
sex,  and  the  appearance  of  the  perfect  insect  does  not 
seem  to  be  influenced  in  any  way  by  the  larval  dimor- 
phism. It  is  noteworthy  that  both  colours  of  dimorphic 
larvae  are  invariably  of  protective  value  :  they  are,  in 
fact,  nearly  always  the  two  chief  tints  of  nature — 
green  and  brown. 

If  we  breed  from  moths  developed  from  the  green 
larvae  of,  e.g.,  the  Large  Emerald,  the  larvae  in  the 
next  generation  are  chiefly  green,  and  after  several 
generations  there  is  little  doubt  that  the  brown  form 
would  become  excessively  rare  ;  so  also  the  green  form 
would  disappear  if  we  bred  from  the  brown  varieties. 
But  in  nature  both  forms  are  common,  and  therefore  it 
is  certain  that  both  must  be  advantageous  to  the  species, 


PROTECTIVE  RESEMBLANCES-DIMORPHISM,   ETC.      47 

or  one  of  them  would  quickly  disappear.  I  -believe 
that  it  is  a  benefit  to  the  species  that  some  of  its 
larvae  should  resemble  brown  and  others  green  catkins, 
instead  of  all  of  them  resembling  either  brown  or  green. 
In  the  former  case  the  foes  have  a  wider  range  of 
objects  for  which  they  may  mistake  the  larvse,  and 
the  search  must  occupy  more  time,  for  equivalent 
results,  than  in  the  case  of  other  species  which  are 
not  dimorphic. 

Dimorphism  is  also  valuable  in  another  way :  the 
widening  range  of  a  species  may  carry  it  into  coun- 
tries in  which  one  of  its  forms  may  be  especially 
well  concealed,  while  in  other  countries  the  other 
form  may  be  more  protected.  Thus  a  dimorphic 
species  is  more  fully  provided  against  emergencies 
than  one  with  only  a  single  form.  To  take  an  ex- 
ample :  the  green  colour  of  the  young  caterpillars  of 
the  Convolvulus  Hawk  Moth  (Sphinx  convolvuli)  some- 
times persists,  and  is  sometimes  replaced  by  brown 
in  the  later  stages.  In  Europe  the  latter  form  pre- 
dominates, because  the  creeping  food-plant  (Con- 
volvulus arvensis)  is  so  small  that  it  is  safer  for  a  large 
caterpillar  to  resemble  the  earth  beneath  rather  than 
the  small  leaves  on  its  surface.  In  the  Canary  Islands 
and  Madeira,  where  the  larva  feeds  on  many  large- 
leaved  species  of  Convolvulus,  the  green  form  pre- 
dominates, for  it  is  far  better  protected  than  the  other 
against  a  continuous  green  background. 

This  result  appears  to  have  been  brought  about  by 


48  THE  COLOURS  OF  ANIMALS 

the  ordinary  operation  of  natural  selection,  leading  to 
the  extermination  of  the  less  protected  variety.  I 
have  experimented  with  all  the  dimorphic  larvae  men- 
tioned above,  and  could  not  find  any  trace  of  suscep- 
tibility to  the  influence  of  surroundings,  so  as  to  lead 
to  the  production  of  the  appropriate  form.  When 
such  susceptibility  is  present,  of  course  the  dimorphism 
has  a  far  higher  protective  value.  The  description  of 
such  cases  is  reserved  for  a  future  chapter. 

Occasionally  the  two  forms  of  a  dimorphic  species 
appear  at  different  times  and  correspond  to  the  tints 
which  successively  predominate  in  the  surroundings. 
At  one  time  I  thought  the  brown  form  of  the  Large 
Emerald  caterpillar  might  appear  rather  later  than 
the  other,  when  the  green  catkins  had  been  replaced 
by  brown ;  but  further  examination  did  not  confirm 
the  observations  which  pointed  in  this  direction.  Dr. 
Alexander  Wallace,  of  Colchester,  has,  however,  found 
that  the  moths  of  Bombyx  cynthia  which  are  the  first 
to  emerge  from  the  pupae  possess,  as  a  rule,  an  olive- 
green  ground  colour,  while  those  which  emerge  in 
September  are  generally  of  a  yellow  tint.  These 
colours  harmonise  with  the  appearance  of  the  Ailanthus 
leaflets  at  corresponding  times  of  the  year. 


Dimorphism  in  the  Perfect  Insect 

Dimorphism  is  also  met  with  in   perfect  insects, 
and  it  is  especially  frequent  in  the  females  (see  page 


PROTECTIVE  RESEMBLANCES— DIMORPHISM,   ETC.      4U 

302  for  an  example  of  a  dimorphic  male  among 
spiders).  Its  meaning  is  obscure,  but  one  of  the  two 
forms  is  generally  much  rarer  than  the  other,  and 
probably  the  older.  The  facts  seem  to  point  towards 
the  replacement  of  an  older  by  a  younger  form, 
because  the  latter  is  more  attractive  to  the  opposite 
sex,  or  because  it  is  better  concealed,  or  because  the 
appearance  is  accompanied  by  other  benefits  to  the 
species.  The  dark  variety  of  the  female  Silver-washed 
Fritillary  (Argynnis  paphia,  var.  ralezina),  and  the 
white  variety  of  the  female  Clouded  Yellow  (Colias 
edma,  var.  helice),  are  examples  of  dimorphism  among 
British  butterflies.  I  exclude  that  form  of  dimor- 
phism, or  polymorphism,  which  is  caused  by  one  sex 
'  mimicking '  two  or  more  species  which  are  specially 
protected  (for  a  good  example  see  pp.  234-38). 

An  extremely  important  form  of  di-  or  poly- 
morphism occurs  among  the  females  of  the  social 
Hymenoptera.  In  this  case,  however,  the  different 
forms  are  specially  fitted  for  certain  duties,  and  the 
consequent  division  of  labour  is  beneficial  to  the 
society  and  therefore  to  the  species. 


Seasonal  Dimorphism 

Finally,  a  species  which  passes  through  two  or 
more  cycles  of  development  in  a  year,  viz.  one  that 
is '  double  '  or  '  treble-brooded,'  is  often  characterised 
by  *  seasonal  dimorphism/  in  which  the  first  brood  is 


50          THE  COLOURS  OF  ANIMALS 

different  in  appearance,  and  often  in  size,  from  the 
later  ones.  Professor  Weismann  has  investigated  this 
question,  and  he  finds  that  while  the  later  broods  can 
be  readily  made,  by  the  application  of  ice  in  the  pupal 
stage,  to  assume  the  form  of  the  first  or  winter  gene- 
ration, the  latter  cannot  be  made  to  assume  the  form 
of  the  summer  brood  by  the  application  of  warmth. 
He  infers  that  such  species  were  single-brooded  in  the 
short  summers  which  succeeded  the  Glacial  Period, 
and  that  the  appearance  was  that  of  the  present  winter 
form.  As  the  summers  became  longer,  other  newer 
generations  with  a  different  appearance  were  added 
(summer  broods),  but  the  species  always  tends  easily 
to  revert  to  the  more  ancient  form.  An  important 
part  of  the  evidence  consists  in  the  proof  that  such 
species  are  now  single-brooded  hi  the  northern  part  of 
their  range,  and  that  the  one  form  is  that  of  the 
winter  brood  of  more  southern  localities.1 

I  have  given  a  very  brief  sketch  of  dimorphism, 
hardly  alluding  to  polymorphism,  which  is  only  an 
extension  of  the  same  principle.  Although  the  subject 
is  only  touched  upon,  enough  has  been  said  to  show 
that  there  are  many  distinct  kinds  of  dimorphism, 
some  of  which  are  very  obscure.  By  far  the  most 
important  kind  of  di-  or  polymorphism  remains  to  be 
described  below  (see  Chapters  VIII.  and  IX.),  in  which 

1  See  Studies  in  the  Theory  of  Descent,  by  August  Weismann. 
English  translation  by  Professor  Meldola. 


PROTECTIVE  RESEMBLANCES— DIMORPHISM,  ETC.      51 

each  individual  has  two  or  more  appearances,  as  it 
were,  at  its  command,  and  can  develop  that  one  which 
is  most  suited  to  its  own  peculiar  surroundings. 


A  reason  for  the  wonderful  concealment  of  Lepidopterous 
larvae 

In  the  remarkable  abundance  and  variety  of 
methods  by  which  concealment  is  effected  in  Lepi- 
dopterous larvae,  we  probably  see  a  result  of  their 
peculiarly  defenceless  condition.  A  larva  is  a  soft- 
walled  cylindrical  tube  which  owes  its  firmness,  and 
indeed  the  maintenance  of  its  shape,  to  the  fact  that 
it  contains  fluid  under  pressure,  which  is  exerted  by 
the  sides  of  the  body.  This  construction  is  extremely 
dangerous,  for  a  slight  wound  entails  great  loss  of 
blood,  while  a  moderate  injury  must  prove  fatal. 
Hence  larvae  are  so  coloured  as  to  avoid  detection  or 
to  warn  of  some  unpleasant  attribute,  the  object  in 
both  cases  being  the  same — to  leave  the  larva  un- 
touched, a  touch  being  practically  fatal  (see  also 
pp.  175-76). 

The  concealment  of  Pupae 

Protective  Resemblance,  either  Special  or  General, 
is  seen  in  nearly  all  exposed  pupae,  but  most  chrysalides 
are  buried  in  the  earth  or  protected  by  cocoons.  The 
cocoons  are  often  sufficient  defence,  because  the  silk  is 
very  unpleasant  in  the  mouth ;  but  such  protection 


52          THE  COLOUES  OF  ANIMALS 

only  applies  in  the  warmer  weather  when  there  is 
an  abundance  of  insect  food.  In  the  winter,  insectivo- 
rous animals  are  pinched  by  hunger,  and  would  devour 
the  pupa  in  spite  of  the  cocoon.  We  therefore  find 
that  all  cocoons  which  contain  pupae  during  the  winter 
are  well  concealed,  either  spun  between  leaves  which 
fall  off  and  become  brown,  or  hidden  under  bark  or 
moss,  or  constructed  on  the  surface  of  bark  with  a 
colour  and  texture  which  renders  them  extremely 
difficult  to  detect.  It  is  very  common  for  particles  of 
the  bark  to  be  gnawed  off  by  the  larva  and  fixed  on  to 
the  outside  of  the  cocoon.  It  will  be  shown  below 
that  many  larvae  can  also  control  the  colour  of  their 
cocoons. 

Protective  Resemblances  in  Butterflies  and  Moths 

The  perfect  insect  is  also  commonly  defended  by 
very  efficient  methods  of  concealment.  The  under 
sides  of  the  wings  of  butterflies  are  generally  coloured 
like  the  surface  on  which  the  "insect  habitually  rests, 
and  they  are  the  only  parts  seen  during  repose.  We 
can  form  some  idea  of  the  perfection  of  this  conceal- 
ment when  we  remember  the  entire  disappearance  of 
common  butterflies  in  dull  weather.  Many  of  them 
creep  far  down  among  thickly  set  leaves,  while  others 
rest  freely  exposed  upon  surfaces  which  harmonise 
with  their  colours. 

Perhaps  the  most  perfect  concealment  attained 
by  any  butterfly  is  seen  in  the  genus  Kallima,  found 


PKOTECTIVE  RESEMBLANCES— DIMORPHISM,   ETC.      53 

in  India,  the  Malay  Archipelago,  and  Africa.  The 
way  in  which  the  insect  is  concealed  has  been  described 
by  Wallace  in  his  '  Malay  Archipelago,'  and  also  in 
the  'Essays  on  Natural  Selection.'  The  tip  of  the 
fore-wing  is  pointed  like  the  apex  of  a  leaf,  and  the 
hind-wing  has  a  short  tail  like  a  leaf-stalk,  while  the 
outline  of  the  folded  wings  between  these  extremities 
is  exactly  like  that  of  a  withered  and  somewhat 
shrivelled  leaf.  At  rest  the  wings  are  held  upright 
over  the  back,  the  head  and  antennae  are  concealed 
between  them,  while  the  tails  touch  the  branch  to 
which  the  insect  clings  by  its  almost  invisible  legs. 
Along  the  supposed  leaf  runs  a  distinct  mark  like 
a  mid-rib,  with  oblique  veining  on  either  side. 

But  dead  and  withered  leaves  are  not  all  alike ; 
they  may  be  almost  any  shade  of  brown,  grey,  or 
yellow,  while  they  are  often  attacked  by  fungi  of  dif- 
ferent colours  and  in  different  places.  Similarly  the 
under  sides  of  the  wings  of  the  butterfly  are  excessively 
variable,  the  different  colours  and  markings  only 
agreeing  in  that  they  all  represent  some  familiar  ap- 
pearance presented  by  withered  or  decayed  leaves. 

Dead  leaves  are  often  pierced  by  insect  larvae,  and 
a  detail  of  great  interest  is  added  to  the  disguise  in 
the  semblance  of  a  small  hole.  The  scales  are  absent 
from  both  sides  of  a  certain  spot  on  each  fore- wing, 
which  is  therefore  only  covered  by  the  thin  transparent 
wing  membrane.  These  spots  come  opposite  to  each 
other  in  the  position  pf  rest,  and  the  effect  produced 
4 


54         THE  COLOUES  OF  ANIMALS 

is  exactly  that  of  a  hole,  for  the  two  membranes  are 
BO  transparent  that  they  are  completely  invisible.  The 
size  of  the  apparent  hole  varies  very  greatly  in  the 
numerous  specimens  of  Kallima  inachis,  in  the  Hope 
Collection  at  Oxford. 

The  upper  sides  of  the  wings,  concealed  during 
rest,  are  dark,  with  a  deep  orange  bar  across  the 
fore-wings.  I  have  heard  a  naturalist,  who  is  ac- 
quainted with  the  Indian  species  (Kallima  inachis)  in 
its  natural  surroundings,  object  to  the  interpretation 
afforded  by  Mr.  Wallace,  on  the  ground  that  he  has 
often  seen  the  butterfly  displaying  the  conspicuous 
upper  sides  of  its  wings  when  settled,  and  has  seen  it 
resting  on  inappropriate  surfaces.  I  do  not  think 
that  this  objection  is  fatal ;  for  butterflies  only  dis- 
play their  brilliant  tints  during  the  short  pauses 
between  the  successive  flights,  when  they  are  on  the 
alert  and  can  evade  their  enemies  by  wariness  and  by 
the  swiftness  of  their  flight.  Our  own  beautiful  Eed 
Admiral  (Vanessa  atalanta),  Peacock  (V.  Jo),  and  Small 
Tortoiseshell  (V.  urticce)  similarly  display  their  bril- 
liant colours  when  pausing  on  a  flower  or  even  on  the 
ground.  But  during  prolonged  rest,  when  the  insects 
are  often  semi- torpid  and  would  be  easily  captured  if 
detected,  the  wing?,  are  invariably  held  so  that  the 
sombre  tints  of  the  under  sides  are  alone  visible. 
Hence  the  display  of  bright  colours  by  the  Indian 
Kallima  is  no  argument  against  the  protective  value 
of  the  leaf-like  appearance  of  the  under  sides ;  for  the 


PKOTECTIVE  RESEMBLANCES— DIMORPHISM,  ETC.      55 

latter  acts  as  a  disguise  when  it  is  most  necessary,  for 
the  butterfly  to  be  concealed.  It  appears  that  the 
Malayan  species  (Kallima  paralekta)  is  more  cautious 
during  the  brief  pauses  between  the  flights ;  for  Mr. 
Wallace  states  that  it  frequents  dry  woods  and  thickets, 
and  that  it  invariably  settles  on  bushes  with  dry  or 
dead  leaves.  He  never  saw  one  of  these  butterflies 
settle  upon  a  flower  or  green  leaf. 

A  recent  paper  by  Mr.  .S.  B.  J.  Skertchly !  en- 
tirely supports  Mr.  Wallace's  statements.  The  author 
calls  attention  to  the  fact  that  leaf-mimicking  butter- 
flies, of  several  genera  in  addition  to  Kallima,  settle 
in  an  entirely  different  manner  from  that  of  other 
butterflies.  While  the  latter  gradually  slacken  their 
speed  and  settle  deliberately,  the  leaf  butterflies  '  fly 
rapidly  along,  as  if  late  for  an  appointment,  suddenly 
pitch,  close  their  wings,  and  become  leaves.  It  is 
generally  done  so  rapidly  that  the  insect  seems  to 
vanish.' 

Certain  English  moths  are  also  protected  by  their 
resemblance  to  dead  leaves.  One  of  the  most  beautiful 
examples  is  afforded  by  the  Herald  Moth  (Gonoptera 
libatrix),  which  suggests  the  appearance  of  a  decayed 
red  leaf  sprinkled  with  a  few  white  spots  of  fungoid 
growth ;  the  irregularly  toothed  margin  of  the  wings 
adds  to  the  effect.  The  bright  eyes  of  the  moth  might 
expose  the  deception,  but  they  are  covered  during 
rest  by  a  tuft  of  hair  which  springs  from  the  base  of 

1  Ann.  and  Mag.  Nat.  Hist.  Sept.  1889,  pp.  209  et  seg. 


56 


THE  COLOURS  OF  ANIMALS 


the  antennae  (see  fig.  14).  When  the  moth  is  about 
to  fly  the  antennae  are  brought  forward,  and  the  same 
action  raises  the  tufts  and  uncovers  the  eyes.  The 
moth  appears  in  the  autumn  and  lives  through  the 
winter,  so  that  the  resemblance  to  dead  leaves  is 
peculiarly  appropriate. 

The  Angle-shades  (Phlogophora  meticulosa)  is  also 
beautifully  concealed  by 
resembling  a  withered 
and  crumpled  leaf.  The 
colours  of  the  Yellow 
Underwing  (Triplicena 
pronuba),  as  seen  during 
flight,  strongly  suggest 
the  appearance  of  a  yel- 
low leaf  whirled  along 
by  the  wind  and  then 
suddenly  dropping.  The 
sudden  swift  rise  and 
rapid  descent  are  very 
unlike  the  flight  of  a 
moth.  When  at  rest,  it  hides  deeply  amid  thick 
foliage  or  among  dead  leaves  on  the  ground ;  it  is 
extremely  difficult  to  detect,  and  instantly  rises  when 
disturbed. 

The  Rev.  Joseph  Greene  has  pointed  out  that  the 
various  shades  of  yellow  and  brown  are  especially 
characteristic  of  autumn  moths,  while  grey  and  silvery 
tints  predominate  in  the  winter  species ;  such  tints 


FIG.  14.— The  base  of  left  antenna  of 
Herald  Moth  (Gonoptera  libatrix),  show- 
ing the  tuft  of  hair  which  covers  the  eyes 
of  the  moth  in  the  position  of  rest ; 
x  24-5  diameters. 


PROTECTIVE  RESEMBLANCES— DIMORPHISM,  ETC.  57 

harmonise  with  those  that  are  most  characteristic  in 
the  corresponding  seasons. 

The  Buff-tip  Moth  (Pyg&ra  bucephala)  is  very 
perfectly  concealed  by  resembling  a  broken  piece  of 
decayed  and  lichen-covered  stick.  The  cylindrical 
shape  is  produced  by  the  wings  being  rolled  round  the 
body.  A  friend  l  has  raised  the  objection  that  the 
moth  resembles  a  piece  of  stick  cut  cleanly  at  both 
ends,  an  object  which  is  never  seen  in  nature.  The 
reply  is  that  the  purple  and  grey  colour  of  the  sides  of 
the  moth,  together  with  the  pale  yellow  tint  of  the  parts 
which  suggest  the  broken  ends,  present  a  most  perfect 
resemblance  to  wood  in  which  decay  has  induced  that 
peculiar  texture  in  which  the  tissue  breaks  shortly 
and  sharply,  as  if  cut,  on  the  application  of  slight 
pressure  or  the  force  of  an  insignificant  blow. 

The  excreta  of  birds  are  also  very  commonly  re- 
sembled by  moths  as  well  as  by  caterpillars.  This 
is  the  case  with  the  little  Chinese  Character  (Cilix 
spinula}?  and  with  many  grey  and  white  Geometers 
which  rest  on  the  upper  sides  of  leaves  with  their 
wings  extended  as  if  '  set.'  In  this  position  they 
forcibly  suggest  the  appearance  of  birds'  excrement 
which  has  fallen  on  to  a  leaf  from  a  great  height,  and 
has  therefore  become  flattened  into  a  wide  patch.  In 
spite  of  a  faithful  resemblance  to  such  an  object,  these 
moths  possess  very  great  beauty. 

»  Dr.  C.  M.  Chadwick,  of  Leeds. 

*  Arthur  Sidgwick,  Journ.  of  the  Rugby  School  Nat.  Hist.  Soc. 


58          THE  COLOUKS  OF  ANIMALS 

The  appearance  of  splinters  of  wood  is  also  often 
suggested  by  moths  such  as  the  '  Sharks '  (Cucullia) 
or  Goat  Moth  (Cossus).  Others  resemble  the  surfaces 
of  rock  upon  which  they  habitually  rest  (Bryophila, 
many  Geometers,  &c.). 

I  have  merely  given  a  few  striking  instances  of 
resemblance  to  objects  which  are  of  no  interest  to 
insect-eating  animals.  Numerous  other  examples 
might  have  been  added,  but  my  object  is  merely  to 
illustrate  from  the  Lepidoptera  a  principle  of  colour- 
ing which  is  of  extremely  wide  application,  viz.  its 
use  in  aiding  an  organism  to  escape  from  enemies 
by  the  method  of  concealment.  Abundant  examples 
of  this  principle  will  be  recognised  by  every  one 
interested  in  natural  history,  among  other  orders  of 
insects  as  well  as  the  Lepidoptera,  among  vertebrate 
animals  no  less  than  among  the  invertebrate  sub- 
kingdoms. 


Protective  Resemblances  in  other  Insects  and  in  Spiders 

In  the  other  orders  of  insects,  the  Orthoptera 
(locusts,  grasshoppers,  &c.)  will  be  found  to  include  the 
most  beautiful  examples  of  Protective  Eesemblance. 
The  tropical  '  leaf  insects '  and '  walking-stick  insects ' 
belong  to  this  order.  The  latter  hold  their  limbs 
irregularly,  so  that  the  resemblance  to  a  dead  branch 
with  lateral  twigs  is  rendered  all  the  more  perfect. 


PEOTECTIVE  RESEMBLANCES-DIMORPHISM,  ETC.      59 

Spiders  are  often  protectively  coloured ;  many  ex- 
cellent examples  are  given  by  Elizabeth  G.  Peckham.1 
One  of  the  most  remarkable  is  Ccerostris  mitralis,  from 
Madagascar,  which  sits  motionless  on  a  branch  and 
resembles  a  woody  knot.  Its  appearance  is  shown  in 
fig.  15.  A  common  Wisconsin  spider,  Epeira  prompta, 


FIG.  15.— Cceroslris  mitralis  in  proaie;        FIG.  IS.—Speir 

from  Peckham  ;  after  Vinson.  lichen  -  covered"  tree"-  trunk  ;     from 

Peckham. 

generally  rests  on  the  branches  of  cedar  bushes,  and 
closely  resembles  lichen  (see  fig.  16).  Spiders  are 
especially  relished  by  insectivorous  animals,  so  there 
is  every  reason  for  the  faithfulness  of  these  resem- 
blances. In  many  other  cases,  however,  the  resem- 
blance is  chiefly  aggressive,  enabling  the  spider  to 
approach  its  prey. 

1  Occasional  Papers  of  tJie  Natural  History  Society  of  Wisconsin, 
vol.  i.  1889,  Milwaukee,  pp.  61  et  seq. 


60  THE  COLOURS  OF  ANIMALS 


CHAPTEE  V 

PROTECTIVE  RESEMBLANCES  IN  VEETE- 
BE  AT  A,  ETC. 

MANY  of  the  lower  Vertebrata  have  the  power  of 
rapidly  modifying  their  colour  according  to  the  en- 
vironment, and  these  will  be  described  in  a  future 
chapter.  Such  a  power  appears  to  be  possessed  by 
few  reptiles,  and  by  no  bird  or  mammal. 


Protective  Resemblances  among  Reptiles 

Our  two  English  snakes  are  well  concealed  by 
their  colours ;  the  olive-green  Grass  Snake  (Tropi- 
donotus  natrix)  harmonising  well  with  the  grassy  banks 
which  it  chiefly  frequents;  while  the  brown  viper 
(Pelias  berus)  is  difficult  to  detect  upon  the  dry  heaths 
where  it  is  most  commonly  found.  Our  lizards  are 
also  well  protected  in  the  same  manner. 

Protective  Resemblances  among  Birds 

Wallace  has  directed  attention  to  the  protective 
colours  of  female  birds  which  build  open  nests,  and  he 
points  out  that  the  males  are  similarly  protected  when 


PROTECTIVE  RESEMBLANCES  IN  VERTEBRATA   61 

they  undertake  the  duties  of  incubation.  The  same 
necessity  does  not  apply  to  species  which  construct 
covered  nests  or  build  in  holes. 


The  Colours  and  Markings  of  Birds'  Eggs 

The  protective  value  of  the  tints  and  markings 
of  eggs  are  of  great  interest,  and  have  not  been 
sufficiently  investigated.  The  fact  that  eggs  are 
protectively  coloured  was  fully  recognised  by  Erasmus 
Darwin,  who  places  them  under  '  colours  adapted  to 
the  purpose  of  concealment.'  He  says  '  the  eggs  of 
birds  are  so  coloured  as  to  resemble  the  colour  of 
the  adjacent  objects  and  their  interstices.  The  eggs 
of  hedge-birds  are  greenish  with  dark  spots;  those 
of  crows  and  magpies,  which  are  seen  from  beneath 
through  wicker  nests,  are  white  with  dark  spots ;  and 
those  of  larks  and  partridges  are  russet  or  brown,  like 
their  nests  or  situations.' l  This  description  of  the 
eggs  of  crows  and  magpies  is  incorrect.  The  eggs 
of  crows  are  greenish  with  umber  markings;  those 
of  magpies  pale  greenish  with  dark  markings.  It  is 
probable  that  Erasmus  Darwin  correctly  explained 
the  appearance  of  the  eggs  of  the  wood-pigeon  (see 
p.  62),  and  inadvertently  illustrated  this  principle  of 
colouring  by  erroneous  instances.  The  special  men- 
tion of  the  interstices  between  the  parts  of  sur- 
rounding objects,  as  well  as  the  objects  themselves,  is 

1  Zoonomia,  1794,  vol.  i.  p.  510. 


62         THE  COLOURS  OF  ANIMALS 

of  great  interest;  protective  colouring  can  never  be 
fully  understood  until  this  principle  is  taken  into 
account. 

In  order  to  make  out  the  true  meaning  of  the 
colours  of  eggs  they  must  be  observed  in  their  natural 
surroundings,  and  must  be  looked  at  from  all  points 
of  view  and  at  varying  distances.  It  is  very  probable 
that  the  bright  blue  colour  of  certain  eggs  will  be 
explicable  under  these  conditions. 

The  fact  that  concealed  eggs  are  almost  invariably 
white  strongly  confirms  the  conclusion  that  the  colours 
of  expos-ed  eggs  are  of  value  to  the  species,  and  are 
maintained  by  the  operation  of  natural  selection. 
Certain  exposed  eggs  may,  however,  be  white,  as  in 
the  wood-pigeon,  but  in  these  cases  the  eggs  are  pro- 
tected from  enemies  beneath ;  for  the  holes  in  the 
loosely  constructed  nest  through  which  they  are  seen 
cannot  be  distinguished  from  others  through  which 
the  bright  sky  appears. 

The  whiteness  of  eggs  hidden  in  holes  or  in  covered 
nests,  or  buried  under  leaves,  is  of  a  very  different 
nature,  for  it  is  due  to  the  cessation  of  natural  selec- 
tion, perhaps  aided  by  reversion  to  the  ancestral 
colour,  which  is  still  preserved  in  the  eggs  of  reptiles. 
All  useful  characters  are  kept  up  to  a  high  pitch  of 
efficiency  by  the  continual  elimination  of  the  unfittest, 
and  as  soon  as  such  elimination  ceases,  the  level  of 
efficiency  must  fall.  This  interpretation  is  confirmed 
by  the  fact  that  the  eggs  of  certain  species  which  now 


PROTECTIVE  RESEMBLANCES  IN  VERTEBRATA      63 

nest  in  the  dark  still  retain  traces  of  patterns  which 
are  well  developed  upon  the  eggs  of  their  nearest  allies 
with  other  habits.  Thus  the  egg  of  the  puffin,  which 
nests  in  a  burrow,  would  be  called  white  at  a  little 
distance,  but  closer  examination  reveals  the  presence 
of  very  faint  spots,  which  are  distributed  as  in  the 
very  distinctly  marked  egg  of  the  razor-bill.1  Certain 
other  species  still  lay  strongly  marked  eggs  in  the 
dark,  and  in  their  case  the  change  of  habit  presumably 
took  place  at  a  comparatively  recent  date.  Such  a 
conclusion  can  be  tested  by  an  investigation  of  the 
habits  of  closely  allied  species.  Although  white  must 
have  been  the  ancestral  colour  of  birds'  eggs,  it  has 
probably  been  re-acquired  in  species  which  nest  in  the 
dark.  It  would  be  very  difficult  to  believe  that  such 
a  habit  has  persisted  continuously  since  the  time  when 
all  birds'  eggs  were  white. 

The  strongest  confirmation  of  this  explanation  of 
the  whiteness  of  hidden  eggs  is,  however,  to  be  found 
in  the  colours  of  the  eggs  in  the  various  breeds 
of  domestic  fowls.  If  the  gradual  disappearance  of 
colour  is  due  to  the  cessation  of  natural  selection,  we 
must  expect  it  to  occur,  however  the  cessation  has 
been  brought  about.  Natural  selection  cannot  operate 
to  preserve  the  colour  of  eggs  laid  in  the  dark,  and  it 

1  This  interesting  example  attracted  my  attention  while  looking 
over  a  collection  of  eggs  in  the  possession  of  my  friend,  Mr.  E.  H. 
Greenly.  Mr.  H.  Seebohm  informs  me  that  he  has  no  doubt  about 
the  validity  of  this  interpretation,  which  was  suggested  in  hiu  work 
on  British  Birds,  1885,  vol.  iii.  p.  367. 


64         THE  COLOUES  OF  ANIMALS 

is  equally  inoperative  when  enemies  are  artificially 
excluded  from  eggs  laid  in  open  nests.  And  the  eggs 
laid  in  our  poultry-yards  afford  conclusive  evidence 
that  colour  disappears  as  surely  under  the  latter 
condition  as  under  the  former.  The  brown  colour 
must  be  a  very  important  protection  to  the  eggs  of 
the  ancestor  of  our  domestic  breeds,  the  Asiatic  jungle 
fowl  (Gallus  bankiva) ;  while  a  white  appearance 
would  greatly  add  to  the  danger  of  discovery  by  egg- 
eating  animals.  But  there  is  no  such  difference  be- 
tween the  value  of  white  and  brown  in  confinement, 
and  we  accordingly  find  that  the  colour  is  disappear- 
ing. Certain  fowls  lay  white  eggs,  and  the  tint  of 
those  which  still  lay  coloured  eggs  varies  considerably, 
'  the  Cochins  laying  buff-coloured  eggs,  the  Malays  a 
paler  variable  buff,  and  Games  a  still  paler  buff.  It 
would  appear  that  dark-coloured  eggs  characterise  the 
breeds  which  have  lately  come  from  the  East,  or  are 
still  closely  allied  to  those  now  living  there.' ' 

Erasmus  Darwin  further  suggested  that  the  colours 
of  eggs,  in  common  with  other  protective  colours,  may 
be  due  to  the  effect  of  the  imagination  of  the  female.2 
This  suggestion  has  been  still  further  elaborated  by 
A.  H.  S.  Lucas,3  but  no  real  proof  of  it  is  brought 
forward  in  his  paper.  That  eggs  resemble  their  sur- 


1  Darwin,  Variation  of  Animals  and  Plants  under  Domesti  atiou, 
1875,  vol.  i.  p.  261. 

2  Loc.  cit.  p.  611. 

»  Royal  Society  of  Victoria,  1887,  pp.  52-60. 


PROTECTIVE  RESEMBLANCES  IN  VERTEBRATA      65 

roundings  is  explicable  by  the  operation  of  natural 
selection,  while  the  gradual  loss  of  colour  when  natural 
selection  ceases  to  operate,  is  in  opposition  to  Mr. 
Lucas's  hypothesis,  which  assumes  that  the  colour  of 
the  shell  is  determined  by  the  influence  of  surround- 
ing tints  upon  the  retina  of  the  female.  If  the  rusty 
spots  on  the  eggs  of  birds  of  prey  are  due,  as  Mr. 
Lucas  supposes,  to  the  sight  of  blood,  eggs  laid  in  the 
dark  should  still  be  affected  by  the  memory  of  some 
colour  either  predominant  in  the  surroundings,  or  of 
especial  interest  to  the  female.  The  hypothesis  might 
easily  have  been  tested  by  surrounding  birds  with  un- 
usual colours  and  observing  the  tints  of  their  eggs : 
and,  had  this  been  done,  I  believe  that  the  paper  would 
not  have  been  written. 

Since  the  last  paragraph  was  printed,  a  letter  from 
the  Rev.  F.  F.  Grensted  has  been  communicated  to 
'  Nature '  by  Mr.  A.  E.  Wallace.1  The  writer  believes 
that  the  colour  of  the  egg  of  the  red-backed  shrike 
varies  with  the  tint  of  the  lining  material  of  the  nest. 
Mr.  E.  B.  Titchener  maintains  that  there  is  not  suffi- 
cient evidence  for  this  opinion.  At  one  time  Mr. 
Titchener  believed  that  Variable  Protective  Resem- 
blance was  exhibited  by  the  eggs  of  the  yellow- 
hammer  and  spotted  fly- catcher  as  well  as  by  those 
of  the  red-backed  shrike.  Further  observation  con- 
vinced him  that  the  evidence  was  insufficient.2 

1  Nature,  vol.  41,  Nov.  21,  1889,  p.  53. 

2  Ibid.,  Dec.  12,  1889,  pp.  129-30. 


66         THE  COLOURS  OF  ANIMALS 

The  strongest  argument  used  by  Mr.  Lucas  is  the 
fact  that  cuckoos  at  first  sight  appear  to  have  the 
power  of  adjusting  the  colour  of  their  eggs  to  those  of 
the  birds  which  are  so  successfully  imposed  upon.  It 
seems  to  be  certain,  however,  that  the  cuckoo  carries 
her  egg  to  the  nest  in  her  beak ;  for  there  are  numerous 
instances  of  the  cuckoo's  egg  having  been  found  in 
a  nest  which  the  bird  itself  could  not  possibly  enter, 
and  Mr.  Lucas  gives  examples  of  the  same  kind  from 
Australia.  The  cuckoo  has  therefore  the  chance  of 
seeing  the  colour  of  her  egg,  and  of  carrying  it  to  the 
appropriate  nest.  It  is  also  possible  that  different 
individuals  lay  eggs  of  a  different  shade,  and  deposit 
them  in  the  nests  of  species  with  eggs  of  a  correspond- 
ing appearance.  The  whole  relation  of  the  cuckoo  to 
the  birds  it  deludes  is  most  interesting,  but  very 
difficult  to  decide  satisfactorily,  because  of  the  extreme 
shyness  of  the  bird.  I  do  not  think,  however,  that  the 
facts  which  .are  now  at  our  disposal  afford  sufficient 
justification  for  the  opinion  that  the  female  cuckoo 
can  control  the  colour  of  her  eggs. 

I  have  discussed  the  colours  of  birds'  eggs  at  some 
length  in  the  hope  that  those  readers  who  are  interested 
in  the  subject  may  be  induced  to  observe  for  them- 
selves, and  assist  in  obtaining  a  far  more  complete 
knowledge  of  the  meaning  of  the  colour  and  marking 
of  eggs  than  we  at  present  possess. 

I  know  of  no  more  inspiring  subject  than  the 
colours  of  birds'  eggs.  The  most  superficial  glance 


PBOTECTIVE  RESEMBLANCES  IN  VERTEBRATA  67 

over  a  collection  of  eggs  reveals  hosts  of  interesting 
problems  which  require  solution.  I  look  forward  to 
the  time  when  any  description  of  colour  and  marking 
will  be  considered  incomplete  unless  supplemented 
by  an  account  of  their  meaning  and  importance  in 
the  life  of  the  species. 


Protective  Resemblances  among  Mammalia 

Among  the  Mammalia  it  would  be  hardly  possible 
to  meet  with  a  better  example  of  protective  colouring 
and  attitude  than  that  of  the  hare  as  it  sits  motion- 
less, exactly  resembling  a  lump  of  brown  earth,  for 
which  indeed  it  is  frequently  mistaken.  The  dark 
brown  or  grey  colours  of  all  our  smaller  quadrupeds 
are  also  highly  protective.  The  change  of  colour  in 
northern  mammals  in  the  winter  will  be  described 
in  Chapter  VH 

Protective  Resemblances  among  Fish 

The  power  of  colour  adjustment  is  very  widely 
distributed  among  fish  and  Amphibia,  and  will  receive 
attention  in  a  later  chapter.  I  will  therefore  only  say 
a  few  words  about  the  Protective  Eesemblance  of  the 
former. 

Professor  Stewart  has  shown  me  a  beautiful  ex- 
ample in  the  Australian  Sea  Horse  (Phyllopteryx  eques), 
a  fish  which  is  covered  with  numerous  cutaneous 


68  THE  COLOUKS  OF  ANIMATE 

appendages,  most  of  which  are  supported  by  a  bony  core. 
The  appendages  are  flat,  and  are  alternately  banded 
with  dusky  brown  and  orange,  exactly  resembling  the 
form  and  colour  of  the  sea-weed  to  which  the  fish 
clings  with  its  tail.  There  also  are  many  bony  spines 
without  the  flat  folds  of  skin,  and  these  are  doubtless 
defensive. 

The  general  arrangement  of  colour  on  porpoises, 
most  fish,  &c.,  has  been  well  explained  by  Wallace. 
Looking  down  on  the  dark  back  of  a  fish  it  is  almost 
invisible,  while,  to  an  enemy  looking  up  from  below, 
the  light  under-surface  would  be  equally  invisible 
against  the  light  of  the  clouds  and  sky.'1 

The  white  colour  of  one  side  of  such  fish  as  the 
sole,  turbot,  &c.  (Pleuronectidce),  viz.  the  side  which 
is  in  contact  with  the  sand  or  mud,  cannot  be  ex- 
plained in  this  way.  In  such  a  case  we  see  the  dis- 
appearance of  colour  in  consequence  of  the  cessation 
of  natural  selection,  as  in  the  white  eggs  laid  in  the 
dark,  while  the  white  bellies  of  many  fish  may  be 
compared  to  the  whiteness  of  the  eggs  of  the  wood- 
pigeon,  an  appearance  produced  by  the  operation  of 
natural  selection. 

It  has  been  already  pointed  out  that  natural 
selection  may  not  only  remove  the  pigment  from  an 
animal,  but  may  oven  replace  the  red  blood  of  a 
vertebrate  by  a  colourless  fluid.  The  transparency 

1  Tropical  Nature,  p.  171. 


PROTECTIVE  RESEMBLANCES  IN   VERTEBRATA      69 

of  the  surface  swimming  fish,  Leptocephalus,  is  in- 
creased in  this  way.1 

Protective  Resemblances  among  Marine  Animals 
Before  leaving  this  part  of  the  subject  I  must 
allude  to  Protective  Eesemblances  among  marine 
animals.  Although  large  numbers  of  isolated  cases 
are  understood,  the  principles  of  colouring  in  marine 
forms  have  been  very  incompletely  worked  out.  The 
difficulties  are  far  greater  than  in  land  animals,  be- 
cause it  is  often  nearly  impossible  to  observe  the 
species  in  their  natural  environment,  and  it  has 
been  already  shown  that  this  is  essential  if  we  are  fully 
to  understand  the  meaning  of  all  details  in  their 
appearance  and  attitudes.  It  is,  however,  very  satis- 
factory to  know  that  the  whole  subject  of  the  colouring 
of  marine  mollusca  is  being  undertaken  in  a  syste- 
matic manner  by  Mr.  W.  Garstang,2  assisted  by  all  the 
appliances  of  the  laboratory  of  the  Marine  Biological 
Association  at  Plymouth. 

Protective  Resemblances  among  Marine  Mollusca 

E.  S.  Morse  has  shown,  contrary  to  Darwin's 
opinion,3  that  the  appearances  of  many  mollusca 
are  such  as  to  afford  concealment.  An  extremely 

1  E.  Ray  Lankester,  «  On  the  Distribution  of  Haemoglobin,'  Proc. 
Boy.  Soc.  No.  140,  1873. 

2  Journ.  Mar.  Biol.  Assoc.,  New  Series,  vol.  i.  No.  2,  Oct.  1839, 
pp.  173  et  seq. 

3  Descent  of  Man,  vol.  i.  p.  316. 


70  THE  COLOURS  OF  ANIMALS 

interesting  example  was  brought  before  me  by  Mr. 
Garstang,  viz.  that  of  the  Opisthobranch  mollusc, 
Hermcea,  which  is  transparent  and  therefore  invisible, 
except  for  the  '  hepatic '  canals,  which  simulate  in  form 
and  colour  the  reddish  weed  (Griffithsia)  on  which  the 
animal  usually  lives.  Mr.  Garstang  finds  that  the 
colour  is  purely  adventitious,  being  due  to  the  food 
undergoing  digestion  (see  pp.  79,  80).  Another  English 
species  of  Hermcea  is  green,  and  lives  on  green  weeds. 
Mr.  H.  L.  Osborn  has  published  a  very  interesting 
note  on  the  resemblance  between  the  colour  of  a  coral 
on  the  North  American  coast  and  the  mollusc  which 
habitually  lives  upon  it.1  He  states  that  Dr.  E.  B. 
Wilson,  working  in  1879  in  Dr.  Brooks's  laboratory 
at  Beaufort,  N.C.,  found  an  orange-yellow  coral 
(Leptogorgia  virgulata)  invariably  attended  by  a  gastro- 
pod of  the  same  Colour  (Ovulum  uniplicaturri),  which 
was  never  seen  apart  from  the  coral.  Dr.  Wilson's 
coral  occurred  in  shallow  water.  In  1884,  Mr.  Osborn, 
also  working  at  Beaufort,  found  a  Leptogorgia  in  ten 
fathoms  of  water,  of  the  same  general  habit  as  L.  vir- 
gulata, but  of  a  deep  rose  colour,  almost  purple.  The 
ground-colour  was  mottled  with  white  round  the  open- 
ings of  the  polypes.  A  large  number  of  molluscs  were 
found  on  the  coral,  and  these  had  red-brown  shells,  with 
the  surrounding  skin  of  a  deep  rose  colour  mottled  with 
white.  Except  for  this  difference  in  colour  the  molluscs 
exactly  resembled  0.  uniplicatum,  and  Mr.  Osborn  con- 
1  H.  L.  Osborn,  Science,  New  York,  1885,  vi.  pp.  9-10. 


PROTECTIVE  RESEMBLANCES  IN  VERTEBRATA      71 

eiders  that  they  were  undoubtedly  of  the  same  species. 
When  placed  in  an  aquarium  the  molluscs  always 
sought  their  own  corals,  but  if  red-  molluscs  and 
yellow  corals  were  put  together  the  former  took  no 
notice  of  the  latter. 

It  is  very  interesting  to  find  that  Mr.  Garstang 
notices  a  similar  association  between  species  allied  to 
the  above  at  Plymouth.  A  reddish  coral  (Gorgonia 
verrucosd)  is  attended  by  a  gastropod  (Ovula  patula) , 
adapted  in  form  and  colour  for  concealment  on  the 
stems  of  the  Gorgonia. 

It  might  be  argued  that  these  are  cases  of  Pro- 
tective Mimicry,  inasmuch  as  one  animal  resembles 
a  portion  of  another  for  the  purpose  of  protection. 
Similar  examples  are  to  be  found  in  certain  parasites 
which  resemble  the  colour  of  the  hair  or  skin  of 
the  animal  they  infest.  Protective  Mimicry,  how- 
ever, leads  one  animal  to  be  mistaken  for  another, 
and  thus  to  live  upon  the  reputation  of  the  latter. 
Protective  Kesemblance  simply  renders  an  animal 
difficult  to  detect.  Animals  defended  in  the  former 
manner  are  almost  invariably  conspicuous ;  in  the 
latter  they  are  admirably  concealed.  Mr.  Garstang 
tells  me  that  Gorgonia  is  exempt  from  the  attacks  of 
fishes,  so  that  the  molluscs  gain  additional  advantage 
by  resembling  an  inedible  form.  Inasmuch  as  con- 
cealment appears  to  be  the  chief  object  of  the  form  and 
colour,  the  example  falls  under  Protective  Eessmblance, 
although  it  leads  in  the  direction  of  true  Mimicry. 


72          THE  COLOUKS  OF  AKIMALS 


CHAPTER  VI 

AGGRESSIVE  RESEMBLANCES— ADVENTITIOUS 
PROTECTION 

Aggressive  Resemblances 

PASSING  now  to  Aggressive  Resemblances,  the  appear- 
ance of  the  larger  Carnivora  harmonises  well  with 
their  surroundings,  enabling  them  to  approach  their 
prey.  The  colours  of  snakes,  lizards,  and  frogs  are 
doubtless  Aggressive  as  well  as  Protective.  Certain 
carnivorous  insects,  such  as  the  Mantidae,  are  well- 
concealed  by  their  colour ;  and  this,  although  chiefly 
Protective,  is  probably  also  of  value  in  enabling  them 
to  creep  upon  their  prey.  Aggressive,  like  Protective, 
colouring  may  be  either  Special  or  General. 


Alluring  Colouration 

Special  Aggressive  Resemblance  sometimes  does 
more  than  hide  an  animal  from  its  prey ;  it  may  even 
attract  the  latter  by  simulating  the  appearance  of 
some  object  which  is  of  special  interest  or  value  to  it. 
Such  appearances  have  been  called  Alluring  Coloura- 


AGGRESSIVE  RESEMBLANCES,  ETC.  73 

tion  by  Wallace,  and  they  are  some  of  the  most  in- 
teresting of  all  forms  of  Aggressive  Eesemblance. 

An  Asiatic  lizard,  Phrynocephalus  mystaceus,  is  a 
good  example.  Its  general  surface  resembles  the 
sand  on  which  it  is  found,  while  the  fold  of  skin  at 
each  angle  of  the  mouth  is  of  a  red  colour,  and  is 
produced  into  a  flower-like  shape  exactly  resembling 
a  little  red  flower  which  grows  in  the  sand.  Insects, 
attracted  by  what  they  believe  to  be  flowers,  approach 
the  mouth  of  the  lizard,  and  are  of  course  captured. 
Professor  C.  Stewart  kindly  brought  this  instance 
before  me,  and  showed  me  a  specimen  of  the  lizard 
in  the  Museum  of  the  Royal  College  of  Surgeons. 
'  Similar  examples  are  to  be  found  among  fishes. 
The  Angler,  or  Fishing  Frog  (Lophius  piscatorius) ,  pos- 
sesses a  lure  in  shape  of  long  slender  filaments,  the 
foremost  and  longest  of  which  has  a  flattened  and 
divided  "extremity.  The  fish  stirs  up  the  mud  so  as 
to  conceal  itself,  and  waves  these  filaments  about : 
small  fish  are  attracted  by  the  lure,  mistaking  it  for 
worms  writhing  about  in  the  muddy  water ;  they 
approach  and  are  instantly  engulphed  in  the  enormous 
mouth  of  the  Angler.  This  interesting  habit  has  been 
known  since  the  days  of  Aristotle.  Certain  deep-sea 
forms  allied  to  Lophius  behave  in  a  similar  manner, 
but  as  the  depths  of  the  sea  are  dark,  they  have  a 
special  '  phosphorescent  organ,  which  probably  illu- 
minates the  play  of  the  tentacles  which  serve  to 
allure  other  creatures.'  In  some  of  these  fish  (certain 


74  THE  COLOURS  OF  ANIMALS 

species  of  Ceratias)  the  foremost  tentacle  bears  a 
luminous  organ  which  is  suspended  as  a  lure  in  front 
of  the  mouth.1  The  prey  are  attracted  by  the  light 
into  this  convenient  position  for  effecting  their  capture. 
An  Indian  Mantis  (Hymenopus  Ucornis)  feeds 
upon  other  insects  which  it  attracts  by  its  flower-like 


PIG.  n.—Bymenopui  bicomis  in  active  pupa  stage. 

shape  and  pink  colour.  The  apparent  petals  are  the 
flattened  legs  of  the  insect.  The  appearance  of  the 
Mantis  in  the  active  pupa  stage  is  shown  in  fig.  17.- 
The  figure  has  been  copied  from  a  drawing  sent  by 

1  A.  Giinther,  Challenger  Reports,  vol.  xxii.  p.  52,  and  Introduc- 
tion, p.  xxx.  The  function  of  the  luminous  organ  was  first  sug- 
gested by  Liitken. 


AGGRESSIVE  RESEMBLANCES,   ETC.  75 

Mr.  Wood-Mason  to  Mr.  Wallace,  who  kindly  lent  it 
to  me. 

Another  beautiful  example  of  Alluring  Colouring 
was  discovered  by  Mr.  H.  0.  Forbes  in  Java.  Butter- 
flies are  often  attracted  by  the  excreta  of  birds,  and  a 
spider  (Ornithoscatoides  decipiens)  takes  advantage  of 
this  fact  to  secure  its  prey.  The  resemblance  to  a 
bird's  dropping  on  a  leaf  is  carried  out  with  extraordi- 
nary detail.  Such  excreta  consist  of  a  *  central  and 
denser  portion,  of  a  pure  white  chalk-like  colour, 
streaked  here  and  there  with  black,  and  surrounded 
by  a  thin  border  of  the  dried  up  more  fluid  part, 
which,  as  the  leaf  is  rarely  horizontal,  often  runs  for 
a  little  way  towards  the  margin '  and  there  evaporates, 
forming  a  rather  thicker  extremity.  The  margin  is 
represented  by  a  film-like  web,  with  a  thickened  part 
to  represent  the  fluid  which  has  run  to  the  edge  or 
apex  of  the  leaf ;  the  central  mass  is  represented  by 
the  spider  itself  with  white  abdomen  and  black  legs, 
lying  on  its  back  in  the  middle  of  the  web,  and  held 
in  position  by  the  spines  on  its  anterior  legs  which 
are  thrust  under  the  film.1  The  whole  combination  of 
habits,  form,  and  colouring  afford  a  wonderful  example 
of  what  natural  selection  can  accomplish.  In  such  a 
case  there  is  no  necessity  for  calling  in  the  aid  of  any 
other  principle,  for  the  addition  of  each  new  feature 
and  the  improvement  of  every  detail  would  at  once 

1  H.  0.  Forbes :  A  Naturalist's  Wanderings  in  the  Eastern  Archi- 
pelago, pp.  63-65. 


76  THE  COLOURS  OF  ANIMALS 

give  an  advantage  to  the  possessor  in  the  constant 
struggle  for  food. 


Adventitious  Protection 

Before  proceeding  to  describe  the  power  of  Vari- 
able Protective  Eesemblance  possessed  by  many 
animals,  it  is  necessary  to  point  out  that  effects 
similar  to  those  described  above  may  be  gained  by 
means  which  supplement  the  acquisition  of  any  special 
colour  and  form,  or  which  may  entirely  replace  these 
methods  of  producing  concealment.  Many  animals 
cover  themselves  with  objects  which  are  prevalent  in 
their  surroundings  and  are  of  no  interest  to  their 
enemies.  Sometimes  the  meaning  of  this  habit  is 
concealment  alone,  but  in  other  cases  objects  of  great 
strength  are  selected  and  bound  firmly  together  so 
as  to  form  a  resistant  armour. 

Many  Lepidopterous  larvae  live  hi  cases  made  of 
the  fragments  of  the  substance  upon  which  they  live. 
The  cases  of  the  larvae  of  Clothes  Moths  are  only  too 
well  known ;  those  of  the  Psychidce  are  made  of  leaf 
or  brown  grass  stems.  The  larva  of  the  Essex 
Emerald  Moth  (Geometra  smaragdaria)  covers  itself 
with  a  loose  case  made  of  fragments  of  leaves  spun 
together  with  silk.  The  cocoons  of  Lepidoptera  are 
frequently  concealed  by  containing  fragments  of  wood 
or  bark  gnawed  off  the  surface  on  which  the  cocoon  is 
constructed  (Centra,  Cilix,  Hemerophila,  &c.).  Birds' 


AGGRESSIVE  RESEMBLANCES,  ETC.  77 

nests  are  often  similarly  concealed ;  the  lichen- covered 
nest  of  the  chaffinch  is  an  obvious  instance.  - 

The  well-known  cases  of  Caddice-worms  (Trichop- 
tera)  are  partly  for  concealment  and  partly  for  defence ; 
they  are  built  of  grains  of  sand,  small  shells  (often 
alive),  vegetable  fragments, — in  fact,  of  any  suitable 
objects  which  are  abundant  at  the  bottom  of  the 
stream  in  which  they  happen  to  be. 

Some  of  the  best  examples  are  to  be  found  among 
marine  animals.  Certain  sea-urchins  cover  themselves 
so  completely  with  pebbles,  bits  of  rock,  shell,  &c.,  that 
one  can  see  nothing  but  a  little  heap  of  stones. 

Many  marine  mollusca  have  the  samp  habits, 
accumulating  sand  upon  the  surface  of  the  shell  or 
allowing  a  dense  growth  of  algae  to  cover  them.1  The 
best  example  of  the  kind  was  shown  me  by  Professor 
C.  Stewart,  and  is  all  the  more  interesting  because  of 
the  transition  observed  in  the  habits  of  different  species 
of  the  same  genus,  Xenophora.  Many  of  these  gastro- 
pods include  pieces  of  shell,  rock,  coral,  &c.,  in  the 
edge  of  the  growing  shell.  The  effect  is  probably  to 
obscure  the  junction  between  the  shell  and  the  surface 
on  which  it  rests,  and  thus  to  assist  in  rendering  the 
organism  difficult  of  detection.  Thus  the  growth  of 
the  shell  may  be  traced  by  a  spiral  line  of  included 
fragments  (X.  calculifera) .  In  X.  Solaris  the  habit  is 
only  maintained  during  the  early  stages  of  growth, 

1  E.  S.  Morse:  Proc.  Boston  Soc.  Nat.  Hist,  yol,  xiv.  April  5, 
1871,  p.  7. 

5 


78  THE  COLOUKS  OF  ANIMATE 

and  the  spiral  line  of  fragments  extends  for  a  certain 
distance,  and  is  then  suddenly  replaced  by  spines 
which  are  doubtless  of  value  as  a  defence.  In  X.  cerea 
and  X.  solaroides  the  size  of  the  adventitious  particles 
is  so  great  as  to  nearly  conceal  the  shell,  while  in 
X.  conchyliophora  nothing  can  be  seen  but  a  heap  of 
fragments.  Specimens  of  Xenophora  and  of  the  crabs 
mentioned  below  are  to  be  seen  in  the  Museum  of 
the  Eoyal  College  of  Surgeons,  as  part  of  a  beautiful 
series  intended  by  Professor  Stewart  to  illustrate  the 
various  uses  of  the  colours  of  animals. 

The  tube  of  certain  well-known  marine  worms 
(Terebellida)  is  constructed  of  sand-grains  cemented 
together. 

One  of  the  most  interesting  examples  of  adventi- 
tious protection  is  afforded  by  certain  crabs  (Steno- 
rhynchus,  Inachus,  Pisa,  Mala) ,  which  fasten  pieces  of 
sea-weed,  &c.,  on  their  bodies  and  limbs.  Bateson 
has  watched  the  process  in  Stenorhynchus  and  Inachus. 
1  The  crab  takes  a  piece  of  weed  in  his  two  chelae,  and, 
neither  snatching  nor  biting  it,  deliberately  tears  it 
across,  as  a  man  tears  paper  with  his  hands.  He 
then  puts  one  end  of  it  into  his  mouth,  and,  after 
chewing  it  up,  presumably  to  soften  it,  takes  it  out 
in  the  chelae  and  rubs  it  firmly  on  his  head  or  legs 
until  it  is  caught  by  the  peculiar  curved  hairs  which 
cover  th  m.  If  the  piece  of  weed  is  not  caught  by 
the  hairs,  the  crab  puts  it  back  in  his  mouth  and 
chews  it  up  again.  The  whole  proceeding  is  most 


AGGRESSIVE  EESEMBLANCES,  ETC.  79 

human  and  purposeful.  Many  substances,  as  hydroids, 
sponges,  Polyzoa,  and  weeds  of  many  kinds  and 
co1  our s,  are  thus  used,  but  these  various  substances 
are  nearly  always  symmetrically  placed  on  corre- 
sponding parts  of  the  body,  and  particularly  long, 
plume-like  pieces  are  fixed  on  the  head,  sticking  up 
from  it.  ...  Not  only  are  all  these  complicated 
processes  gone  through  at  night  as  well  as  by  day, 
but  a  Stenorhynchus  if  cleaned  and  deprived  of  sight 
will  immediately  begin  to  clothe  itself  again,  with  the 
same  care  and  precision  as  before.' 1  Bateson  states 
that  Stenorhynchus  does  not  betray  any  disposition  to 
remain  in  an  environment  which  harmonizes  with  its 
dress. 

Adventitious  Colouring 

The  protective  colouring  of  many  animals  may  be 
due  to  the  food  in  some  part  of  the  digestive  tract, 
seen  through  the  transparent  body.  This  is  impor- 
tant in  many  transparent  caterpillars,  such  as  the 
Noctuce,  and  probably  in  many  marine  organisms.  If 
a  larva,  such  as  that  of  the  Angle-shades  (Phlogophora 
meticulosd),  be  fed  on  the  orange- coloured  marginal 
florets  of  the  marigold,  the  passage  of  food  along  the 
alimentary  canal  can  be  distinctly  traced  by  the  pro- 
gressive change  in  the  colour  of  the  caterpillar. 

The  green  colour  of  the  blood  of  most  larvae  is 

1  Journ.  Mar.  Biol.  Assoc.,  New  Series,  vol.  i.  No.  2,  Oct.  1889,  pp. 
213-14. 


80         THE  COLOURS  OF  ANIMALS 

adventitious  in  origin,  having  been  derived  from  the 
chlorophyll  of  the  leaves ;  it  is,  however,  much  modi- 
fied in  constitution  by  the  time  it  reaches  the  blood. 
The  green  colouring  matter  passes  from  the  blood 
into  the  cells  of  the  surface  of  the  body  in  many 
caterpillars,  but  is  re-dissolved  in  the  blood  of  the 
chrysalis.  It  is  then  made  use  of,  in  certain  species, 
to  tinge  the  eggs,  and,  after  this,  is  absorbed  into  the 
body  of  the  young  larvae  which  afterwards  hatch  from 
them,  protecting  them  with  a  green  colour  before  they 
have  had  time  to  acquire  fresh  chlorophyll  from  the 
leaves.  The  passage  of  an  adventitious  colouring 
matter  on  into  a  second  generation  is  a  very  remark- 
able phenomenon.  There  does  not,  however,  seem  to 
be  any  doubt  about  its  occurrence  in  certain  species 
(e.g.  Smerinthus  ocellatus) ,l  and  I  have  a  good  deal  of 
unpublished  evidence  on  the  subject. 

1  See  '  Proceedings  of  Physiological  Society,'  pp.  xxv  and  xxvi, 
in  Journal  of  Physiology,  vol.  viii.  1887. 


CHAPTER  VH 

VARIABLE  PROTECTIVE  RESEMBLANCE 
IN   VERTEBRATA,  ETC. 

PROTECTIVE  Resemblance  in  its  highest  and  most  per- 
fect form  must  not  be  fixed,  but  capable  of  adjustment, 
so  that  the  animal  is  brought  into  correspondence 
with  each  of  the  various  tints  which  successively  form 
its  environment,  as  it  moves  about.  An  active  and 
wide-ranging  animal  will  be  benefited  by  the  power 
of  resembling  the  tints  of  many  different  environments, 
and  by  that  of  changing  its  colour  rapidly. 

More  sluggish  animals  only  require  the  power  of 
bringing  their  appearance  into  harmony  with  a  single 
environment,  although  the  capability  of  adjustment 
is  still  of  great  value,  because  the  environments  of  the 
different  individuals  vary,  at  any  rate  to  a  slight 
extent.  Thus  a  moth  lays  some  of  its  eggs  upon  one 
tree  of  a  certain  shade  of  green,  and  others  upon 
another  with  leaves  of  a  rather  different  shade ;  so  that 
the  caterpillars  would  not  have  same  environment,  and 
would  gain,  by  possessing  the  power  to  adapt  their 
colours.  At  the  same  time  there  would  be  no  im- 


82  THE  COLOUES  OF  ANIMALS 

perative  necessity  for  the  change  to  be  extremely 
rapid. 

In  other  cases  it  will  be  of  advantage  to  the  animal 
to  possess  the  power  of  changing  twice  in  its  life,  once 
for  the  peculiar  surroundings  of  the  caterpillar,  and 
once  for  the  peculiar  surroundings  of  the  chrysalis. 
There  is  indeed  some  ground  for  the  belief  that  in 
certain  cases  the  colours  of  the  perfect  insect  also  may 
be  adjusted  to  correspond  with  the  peculiar  environ- 
ment. 

Variable  Protective  Resemblance  in  Fishes 

Instances  of  the  power  of  rapid  adjustment  are 
very  common,  although  most  people  are  not  aware  of 
them.  Nearly  all  fishermen  know  that  the  trout 
caught  in  a  stream  with  a  gravelly  or  sandy  bottom 
are  light-coloured,  while  those  caught  in  a  muddy 
stream  are  dark.  It  is  also  well  known  that  the  same 
fish  will  soon  change  in  colour  when  it  passes  from  one 
kind  of  background  to  the  other.  Thus  Mr.  E.  D.  Y. 
Pode  tells  me  that  all  the  trout  in  a  stream  near  Ivy 
Bridge  have  become  unusually  light  ever  since  the 
pollution  of  the  stream  by  white  china  clay. 

The  same  facts  are  true  of  many  other  freshwater 
and  sea  fishes.  The  interior  of  a  minnow-can  is 
painted  white  in  order  that  the  bait  may  become  light- 
coloured  and  thus  conspicuous  in  the  dark  water  where 
the  pike  or  perch  is  likely  to  be  found.  The  change 
of  colour  occupies  an  appreciable  time,  and  the  fisher- 


VAEIABLE  RESEMBLANCE   IN   VERTEBRATA,  ETC.      83 

man  knows  that  he  stands  an  extra  chance  of  catch- 
ing his  fish  while  the  bait  remains  unadapted  to  its 
environment.  This  experience  serves  to  prove  in  a 
practical  way  that  the  power  of  changing  the  colour  is 
essentially  protective. 


Variable  Protective  Resemblance  in  Amphibia 

Other  animals  possess  the  same  power.  The  Com- 
mon Frog  (Rana  temporaria)  can  change  its  tints  to  a 
considerable  extent.  Thus  Sir  Joseph  Lister  states 
that  '  a  frog  caught  in  a  recess  in  a  black  rock  was 
itself  almost  black;  but  after  it  had  been  kept  for 
about  an  hour  on  white  flagstones  in  the  sun,  was 
found  to  be  dusky  yellow  with  dark  spots  here  and 
there.  It  was  then  placed  again  in  the  hollow  of  the 
rock,  and  in  a  quarter  of  an  hour  had  resumed  its 
former  darkness.  These  effects  are  independent  of 
changes  of  temperature  .  .  .' l  The  Green  Tree  Frog 
(Hyla  arborea),  so  common  in  the  South  of  Europe, 
is  bright  green  when  seated  among  green  leaves,  but 
becomes  dark-brown  when  resting  on  the  earth  or 
among  brown  leaves.  It  is  very  interesting  to  notice 
that  when  this  frog  turns  brown,  irregular  spots 
become  conspicuous  upon  its  skin,  spots  which  evi- 
dently correspond  to  those  upon  the  Common  Frog 
(Rana),  but  which  are  invisible  when  the  green  tint  is 
assumed. 

1  Lister :  Phil.  Trans.,  1858,  vol.  148,  p.  628. 


84          THE  COLOURS  OF  ANIMALS 


Variable  Protective  Resemblance  in  Reptiles 

The  power  of  Variable  Protective  Eesemblance  is 
therefore  present  among  fish  and  Amphibia,  but  the 
most  remarkable  and  well-known  example  is  afforded 
by  a  reptile,  the  Chamaeleon.  The  rapidity  with 
which  the  change  of  colour  takes  place,  and  the  wide 
range  of  tints  which  the  animal  has  at  its  command, 
have  caused  this  lizard  to  be  regarded  as  a  type  of 
everything  changeable.  But  the  same  power  is  also 
present  in  certain  of  the  South  American  lizards- 
belonging  to  the  family  Iguanidce,  and  it  is  probable 
that  Variable  Protective  Eesemblance  is  much  more 
common  than  has  been  generally  supposed. 

The  changes  of  colour  depend  upon  the  eye 

The  physiological  mechanism  by  means  of  which 
these  rapid  changes  of  colour  are  effected  has  been 
investigated  by  Lister  in  this  country,  by  Briicke  in 
Germany,  and  by  Pouchet  in  France.  At  first  sight 
it  appears  likely  that  the  light  may  directly  determine 
the  distribution  of  colouring  matter  in  the  pigment 
cells  in  or  immediately  beneath  the  skin.  Each  of 
the  various  surroundings  of  an  animal  would,  accord- 
ing to  its  colour,  reflect  light  of  a  certain  constitution, 
and  it  might  well  be  supposed  that  each  kind  of  re- 
flected light  would  produce  a  different  effect  upon  the 


VARIABLE   RESEMBLANCE  IN  VERTEBRATA,   ETC.      85 

pigment  cells.  It  is,  however,  now  well  known  that 
the  action  is  extremely  indirect;  certain  kinds  of 
reflected  light  act  as  specific  stimuli  to  the  eye  of  the 
animal,  and  differing  nervous  impulses  pass  from 
this  organ  along  the  optic  nerve  to  the  brain.  The 
brain  being  thus  indirectly  stimulated  in  a  peculiar 
manner  by  various  kinds  of  reflected  light,  originates 
different  impulses,  which  pass  from  it  along  the  nerves 
distributed  to  the  skin,  and  cause  varying  states  of 
concentration  of  the  pigment  in  the  cells.  The  highest 
powers  of  the  microscope,  assisted  by  ah1  the  varied 
methods  of  histology,  have  failed  to  detect  the  con- 
nection between  the  nerves  and  the  pigment  cells  in 
the  skin,  and  yet  such  connection  appears  to  be  ren- 
dered certain  by  the  fact  that  light  falling  on  the  e$B 
modifies  the  distribution  of  the  pigment  granules. 

The  pigment  cells  in  the  skin  are  often  of  various 
colours,  and  are  'arranged  in  layers,  so  that  very 
different  effects  may  be  produced  by  concentration  in 
certain  cells,  leading  to  the  appearance  of  those  of 
another  colour,  or  to  a  combined  effect  due  to  the 
colours  of  two  or  more  kinds  of  cells. 


Blind  animals  cannot  vary  their  colour  protectively 

It  has  been  shown  by  experiment  that  blinded 
frogs  have  no  power  of  altering  their  colour  so  as  to 
correspond  with  surrounding  tints.  The  same  facts 
also  have  been  proved  in  a  most  interesting  manner 


86  THE  COLOURS  OF  ANIMALS 

by  the  observation  of  living  animals  in  their  natural 
surroundings.  Thus  Pouchet  noticed  that  one  single 
plaice  out  of  a  large  number  upon  a  light  sandy 
surface  was  dark-coloured,  and  thus  unlike  its  sur- 
roundings. Examination  showed  that  this  individual 
was  blind,  and  therefore  unable  to  respond  to  the 
stimulus  of  reflected  light.1 

Another  very  interesting  example  of  the  same  kind 
was  brought  under  my  notice  by  my  friend,  Mr.  H. 
Nicoll.  This  gentleman  had  observed  that  in  addition 
to  the  light- coloured  trout  usually  seen  in  a  chalk 
stream  in  Hampshire  (a  tributary  of  the  Test),  very 
dark  individuals  are  occasionally  met  with.  He  was 
puzzled  for  a  long  time,  but  the  fact  that  the  dark 
fish  could  never  be  induced  to  rise  to  a  fly  finally  led 
him  to  examine  them,  when  he  found  that  they  were 
invariably  blind,  the  crystalline  lens  being  opaque. 
Sometimes  the  fish  were  blind  in  one  eye,  but  this  did 
not  affect  their  colour.  The  darkness  appears  to  come 
on  gradually  with  increasing  blindness,  for  the  depth 
of  the  tint  varies  in  different  individuals,  and  some- 
times only  part  of  the  body  (e.g.  the  tail)  is  affected. 
The  blindness  probably  comes  on  with  age,  for  the 
dark  fish  are  always  large,  generally  between  one  and 
two  pounds  in  weight. 

1  Quoted  by  Semper,  Animal  Life,  International  Scientific  Series, 
pp.  95-9ti. 


VAEIABLE  RESEMBLANCE  IN  VEETEBRATA,  ETC.      87 

The  power  of  varying  the  colour  essentially  protective 

The  protective  value  of  the  change  of  colour  in 
normal  trout  was  especially  well  seen  when  contrasted 
with  these  blind  individuals.  As  it  has  been  some- 
times asserted  that  protection  is  not  the  meaning 
of  resemblance  to  the  environment,  I  was  anxious  to 
observe  so  striking  a  contrast  for  myself.  Mr.  Nicoll 
kindly  gave  me  the  opportunity  of  seeing  the  fish  in 
his  stream,  and  I  can  in  every  way  confirm  his  state- 
ment that  a  person  unaccustomed  to  the  observation  of 
animals  would  certainly  fail  to  detect  any  trout  except 
the  black  ones.  No  one  who  had  the  opportunity  of 
comparing  the  changing  colours  of  the  normal  fish — 
ever  harmonising  with  their  surroundings,— with  the 
unvarying  conspicuous  darkness  of  the  blind  in- 
dividuals, could  hesitate  for  a  moment  in  admitting 
that  concealment  is  the  one  object  of  the  adjustment 
of  colour. 

The  change  of  colour  may  also  be  voluntary  or 
may  follow  from  mental  excitement.  Thus  the  colours 
of  fish  often  become  much  brighter  while  they  are 
feeding.1 

The  food  of  blind  trout 

It  may  be  objected  that  the  dark  fish  still  continue 
to  live  in  the  same  stream  with  the  more  perfectly 

1  For  a  carious  change  of  colour  in  the  conger,  see  Bateson,  Ix. 
pp.  214-15. 


88          THP  COLOURS  OF  ANIMALS 

concealed  individuals.  This  is  sufficiently  explained 
by  the  facts  that  the  waters  are  carefully  preserved, 
and  that  the  blindness  only  comes  on  when  the  fish 
are  large,  and  are  therefore  exposed  to  the  attacks  of 
comparatively  few  enemies. 

Mr.  Nicoll  informed  me  that  the  black  fish  were 
usually  in  very  poor  condition,  and  I  was  very  anxious 
to  ascertain  the  kind  of  food  which  was  still  accessible 
to  them.  We  therefore  caught  two  fine  specimens 
which  were  in  fair  condition.  I  opened  them  and 
found  their  stomachs  quite  full  of  caddice-worms, 
cases  and  all,  together  with  a  few  fresh-water  shrimps 
(Gammarus),  These  animals  are  doubtless  hunted  by 
scent  and  touch,  while  the  insects  on  the  surface  of 
the  water  can  only  be  obtained  by  sight.1 


Loss  of  power  of  varying  colour  in  a  chameleon 
before  death 

The  changes  which  took  place  in  a  chamaeleon  in 
my  possession  probably  show  the  dependence  of  the 
power  of  adjustment  upon  the  state  of  the  nervous 
system.  In  the  summer,  while  the  lizard  was  healthy 
and  had  an  abundance  and  variety  of  insect  food,  it 
was  dark-coloured  by  day,  when  it  rested  on  some 
dark  branches  or  walked  about  in  its  shaded  cage. 
Placed  upon  a  leafy  branch  in  strong  light  it  became 

1  Certain  fish  habitually  seek  their  food  by  the  olfactory  and 
tactile  senses.     See  Bateson,  I.e.  p.  214. 


VAKIABLE  RESEMBLANCE  IN  VERTEBRATA,  ETC.      89 

yellowish-green  in  a  very  short  time,  the  change 
beginning  in  a  few  seconds.  At  night  when  it  was 
asleep  it  became  light  and  straw-coloured.  In  the 
winter  it  died,  probably  on  account  of  the  scarcity 
and  monotony  of  the  only  insect  diet  which  could  be 
obtained  for  it.  For  many  days  before  its  death  it 
became  almost  black  and  lost  all  power  of  changing  its 
colour.  Its  weakened  nervous  system  either  ceased  to 
respond  to  the  influence  of  light,  or  was  unable  to  pro- 
duce any  effect  upon  the  pigment  cells,  which  were  thus 
paralysed,  with  their  pigment  permanently  diffused. 
Green  frogs  also  generally  become  dark  before  they  die. 


Explanation  of  darkness  of  blind  animals 

Some  authorities  have  maintained  that  an  animal 
of  a  kind  which  possesses  the  power  of  altering  its 
colour  should,  when  blind,  become  light-  instead  of 
dark-coloured.  When  the  skin  is  light-coloured  the 
pigment  in  the  cells  is  strongly  contracted,  so  that  the 
coloured  surface  contributed  by  each  cell  occupies  but  a 
small  space,  and  produces  but  little  effect ;  when  the  skin 
is  dark  the  coloured  parts  of  the  cells  are  relaxed,  and 
stretch  out  into  the  long  branching  processes,  so  that 
each  dark  surface  becomes  as  large  as  possible.  The 
latter  is  evidently  the  condition  of  rest,  while  concen- 
tration is  the  state  of  activity.  It  is  therefore  to  be 
expected  that  when  the  coloured  parts  of  cells  are 
cut  off  from  all  stimuli,  they  will  be  permanently 


90  THE  COLOURS  OF  ANIMALS 

relaxed,  so  that  the  skin  will  be  dark ;  and  we  have 
seen  that  such  a  result  actually  occurs.  When  a 
muscle  is  cut  off  from  nervous  stimuli  it  also  enters 
a  condition  of  permanent  rest  or  relaxation.  Thus 
when  the  face  is  paralysed  on  one  side,  the  muscles 
are  relaxed  and  unable  to  balance  the  contraction  of 
those  on  the  other,  so  that  the  face  is  drawn  over 
towards  this  latter  side.  The  contractions  of  a  muscle 
cell  and  those  which  take  place  in  a  pigment  cell  are 
not  essentially  different ;  the  former  are  far  more 
specialised  and  powerful,  but  both  of  them  exhibit 
manifestations  of  that  contractile  power  which  is 
possessed  by  the  simplest  cells.  It  is  therefore  of 
interest  that  both  should  behave  in  a  similar  manner 
when  cut  off  from  the  nervous  system  which  provides 
the  stimuli  under  which  both  normally  contract.  In 
1858,  Sir  Joseph  Lister  showed  that  the  coloured 
part  of  a  pigment  cell  contracts  independently  of  the 
cell  itself.  Cells  are  now  recognised  as  composed  of 
a  network  containing  a  glassy  substance  in  its  meshes ; 
pigment  granules  are  only  contained  in  the  network, 
and,  as  this  contracts,  it  carries  them  inwards  from 
the  long  branching  processes  towards  the  centre  of 
the  ceU. 

Loss  of  colour  in  cave-dwelling  animals 

On  the  other  hand  it  has  been  argued  that  the 
Proteus,  a  blind  amphibian  living  in  the  underground 
rivers  of  Carniola,  and  Carinthia,  is  light-coloured, 


VARIABLE  RESEMBLANCE  IN  VERTEBRATA,  ETC.      91 

and  that  other  blind  animals  living  in  dark  caverns 
are  often  white.  In  the  majority  of  cases  this  result 
is  undoubtedly  due  to  the  gradual  disappearance  of 
the  useless  pigment,  and  not  to  the  excessive  con- 
traction of  the  structures  in  which  it  is  usually  con- 
tained. Just  as  the  useless  eye  has  become  rudi- 
mentary in  these  animals,  so  has  the  useless  colour 
gradually  disappeared  from  the  skin.  The  energy 
necessary  for  the  production  and  maintenance  of  such 
structures  has  been  diverted,  either  wholly  or  in 
part,  to  other  and  more  useful  ends.  In  the  Proteus, 
however,  the  degeneration  is  as  yet  incomplete,  for  the 
skin  still  retains  pigment  cells.  An  individual  now  in 
my  possession  has  gradually  become  much  darker  since 
its  removal  from  the  cave  at  Adelsberg.  It  is  probable 
that  this  result  has  followed  from  the  direct  effect  of 
light  upon  the  skin  ;  for  it  is  known  that  superficial 
pigment  cells  are  sensitive  to  light,  although  the 
changes  of  colour  thus  induced  differ  from  those  caused 
indirectly  through  the  nervous  system,  in  the  absence 
of  any  harmony  with  the  colours  of  the  environment. 
The  skin  of  the  Proteus  is  probably  extremely  sensitive 
to  light.  By  day  the  animal  in  my  laboratory  always 
lies  concealed  beneath  a  plate  at  the  bottom  of  the 
aquarium,  while  ife  comes  out  every  night  and  swims 
freely  about.  As  the  eyes  are  very  degenerate  and 
buried  beneath  the  surface,  it  appears  certain  that  the 
difference  between  light  and  darkness  is  appreciated 
by  the  skin.  W.  Bateson  has  shown  that  blind 


92  THE  COLOURS  OF  ANIMALS 

shrimps  and  prawns  bury  themselves  in  the  sand  by 
day  and  swim  about  at  night,  exactly  like  the  uninjured 
animals.1 

The  seasonal  change  of  colour  in  northern  mammals 

The  well-known  fact  that  many  northern  quad- 
rupeds become  white  in  winter  has  given  rise  to  a 
great  deal  of  discussion  as  to  the  manner  in  which 
the  change  is  brought  about.  Some  have  maintained 
that  the  animals  simply  acquire  a  new  coat  of  white 
hair  which  conceals  the  darker  fur  beneath,  while  the 
long  hairs  of  the  summer  coat  are  believed  to  be  shed. 
Others  believe  that  these  latter  actually  change  and 
become  white,  and  that,  although  an  abundance  of 
new  hairs  also  appear,  nothing  is  shed.  Most  ob- 
servers agree  that  the  white  hair  is  shed  at  the  close 
of  winter  :  this  is  of  course  independently  neces- 
sary, in  order  to  reduce  the  thickness  of  the  winter 
coat. 

I  shall  bring  forward  what  appears  to  be  conclusive 
evidence  that  the  latter  view  is  the  right  one,  at  any 
rate  for  certain  species.  But  however  the  change  is 
brought  about,  it  will  be  rightly  considered  in  this 
part  of  the  subject,  if  it  can  be  proved  that  it  is  called 
up  either  directly  or  indirectly  by  the  stimulus  pro- 
vided by  the  external  conditions,  and  is  not  merely  a 
contemporaneous  change,  harmonising  with  those  in 

1  L.c.  p.  212. 


VARIABLE  RESEMBLANCE   IN   VERTEBRATA,   ETC.      93 

the  surroundings.  The  simplest  view  to  take  of  the 
matter  would  be  to  suppose  that  natural  selection  has 
favoured  an  extra  growth  of  hair  of  a  white  colour  for 
the  winter  season,  so  that  if  an  animal  were  trans- 
ported to  the  equator,  a  similar  change  would  take 
place  at  a  corresponding  time.  If  the  change  was 
thus  merely  contemporaneous  and  without  any  actual 
physiological  relation  to  the  surroundings,  it  would 
require  discussion  in  the  previous  chapters,  for  it 
would  be  precisely  parallel  to  the  darkening  of  the 
larva  of  the  Privet  Hawk  Moth,  which  takes  place 
whether  it  will  descend  upon  brown  earth  with  which 
it  will  harmonise,  or  green  turf  against  which  it  will 
be  conspicuous  (see  pp.  42-43) ,  It  is  possible  that  the 
change  of  certain  purely  Arctic  animals  is  of  this 
kind ;  but  it  must  be  remembered  that  many  such 
animals  range  southward  into  districts  where  the 
white  coat  would  be  conspicuous  in  whiter,  so  that 
the  higher  power  of  Variable  Protective  Resemblance 
would  be  very  beneficial. 

The  question  is,  however,  one  of  evidence,  and  I 
shall  show  that  in  certain  species  the  change  in 
colour  is  physiologically  associated  with  the  conditions, 
like  the  change  in  the  colour  of  a  fish  which  depends 
on  the  reflected  light  entering  its  eye.  A  discussion 
of  the  probable  nature  of  the  physiological  association 
is  better  deferred  until  after  considering  the  evidence. 


94  THE  COLOURS  OF  ANIMALS 


Sudden  change  of  colour  determined  by  sudden 
exposure  to  extreme  cold 

A  classical  experiment  made  by  Sir  J.  Boss,  con- 
siderably over  fifty  years  ago,  seems  decisive  on  the 
above-mentioned  point,  as  far  as  the  species  ex- 
perimented upon  is  concerned.  A  Hudson's  Bay 
Lemming  kept  in  the  cabin,  and  thus  shielded  from 
the  low  temperature,  retained  its  summer  coat  through 
the  winter :  '  It  was  accordingly  placed  on  deck  in  a 
cage  on  February  1,  and  next  morning,  after  having 
been  exposed  to  a  temperature  of  30°  below  zero,  the 
fur  on  the  cheeks  and  a  patch  on  each  shoulder  had 
become  perfectly  white.  On  the  following  day  the 
patches  on  each  shoulder  had  extended  considerably, 
and  the  posterior  part  of  the  body  and  flanks  had 
turned  to  a  dirty  white  ;  during  the  next  four  days  the 
change  continued  but  slowly,  and  at  the  end  of  a  week 
it  was  entirely  white,  with  the  exception  of  a  dark 
band  across  the  shoulders,  prolonged  posteriorly  down 
the  middle  of  the  back.  .  .  .'  No  further  change  took 
place,  and  the  lemming  died  of  the  cold  on  February 
18,  the  thermometer  having  been  between  30°  and 
40°  below  zero  every  night.  'On  examining  the 
skin  it  appeared  that  all  the  white  parts  of  the  fur 
were  longer  than  the  unchanged  portions,  and  that 
the  ends  of  the  fur  only  were  white  so  far  as  they 
exceeded  in  length  the  dark-coloured  fur;  and  by 


VARIABLE  RESEMBLANCE   IN  VERTEBRATA,   ETC.      95 

removing  these  white  tips  with  a  pair  of  scissors  it 
again  appeared  in  its  dark  summer  dress,  but  slightly 
changed  in  colour,  and  precisely  the  same  length  as 
before  the  experiment.'  l 

This  experiment  conclusively  proves, — (1)  that 
the  external  condition  itself  provides  the  cause  which 
brings  the  appropriate  change  in  colour;  for  the 
animal  did  not  change  until  subjected  to  the  con- 
dition ; 2  (2)  that  in  all  probability  the  cause  is  a 
lowered  temperature  acting  upon  the  skin ;  (3)  that 
the  existing  dark  hairs  become  white  at  the  tips ;  for 
we  cannot  well  believe  that  a  fresh  growth  could  have 
overtopped  the  existing  hair  in  a  single  night ;  (4)  that 
the  whitening  hairs  grow  suddenly  and  rapidly. 


Nature  of  the  change  of  colour  in  the  American  Hare 

The  same  conclusions  are  also  supported  by  some 
extremely  careful  observations  conducted  by  F.  H. 
Welch  upon  the  American  Hare  (Lepus  Americanus) 
in  New  Brunswick.3  In  the  latter  district  the  animal 
keeps  its  winter  coat  till  May,  when  it  is  gradually 
shed,  the  change  being  complete  in  June.  The  winter 
coat  gradually  develops  in  October  and  November,  and 

1  Sir  J.  Ross :   Appendix  to  Second  Voyage,  Nat.  Hist.  p.  xiv. 
1835. 

2  This  conclusion  is  also  supported  by  the  fact  that  such  changes 
occur  earlier  when  the  winter  is  exceptionally  early.     Concerning 
the  Alpine  Hare,  see  Tschudi,  Thierleben  der  Alpenwelt,  p.  300. 

»  Proc.  Zool.  Soc.  1869,  p.  228. 


96  THE  COLOURS   OF  ANIMALS 

is  retained  from  December  till  the  end  of  April.  The 
appearance  of  the  back  and  sides  in  summer  is  '  glis- 
tening fawn-colour  interspersed  with  black,  especially 
over  the  vertebral  ridge.'  The  colour  is  conferred  by 
long  thick  hairs  (the  pile)  covering  a  woolly  under- 
growth of  a  slaty  colour. 

Early  in  October  the  first  changes  appear ;  the 
whiskers  become  white  at  the  tip  or  in  some  part  of 
the  shaft,  and  a  few  of  the  longer  hairs  on  the  back 
also  become  white  at  the  tip  or  throughout.  At  this 
time  there  is  no  addition  to  the  summer  coat,  only  a 
change  in  the  colour  of  existing  hairs.  The  changes 
advance  during  November,  and  on  separating  the  fur 
a  new  growth  of  stiff  white  hairs  is  seen  over  the  sides 
and  back  :  these  grow  rapidly,  while  the  long  hairs  of 
the  summer  coat  also  grow  and  become  white  very 
quickly  as  soon  as  the  new  hairs  appear  on  the  surface. 
*  The  shaft  of  the  hair  of  the  new  growth  is  invariably 
white,  a  circumstance  which  renders  it  easily  distin- 
guished from  the  autumnal  hair  in  process  of  change.' 
This  change  is  most  frequent  at  the  tip,  proceeding 
downwards,  but  it  sometimes  begins  in  the  middle, 
and  occasionally  at  the  base.  '  The  whiskers,  which 
apparently  do  not  lengthen  but  merely  alter  in  colour, 
will  demonstrate  each  variety. 

'  Thus  the  whiter  hue  would  appear  to  be  brought 
about  by  a  change  of  colour  in  the  pile  of  the  autumnal 
coat,  combined  with  a  new  hybernal  white  crop,  the 
latter  undoubtedly  playing  no  small  part  in  the 


VARIABLE   RESEMBLANCE  IN  VERTEBKATA,   ETC.      97 

colouring  process  and  in  the  thickening  of  the  fur. 
There  is  no  indication  of  shedding :  an  increase  in 
length  ensues  over  the  whole  body.' 

There  is  considerable  individual  difference  in  the 
time  of  change :  it  sometimes  commences  before  the 
first  fall  of  snow,  indicating  that  the  stimulus  is  the  fall 
of  temperature  affecting  the  skin  rather  than  the 
colour  affecting  the  eyes.  Great  differences  are  seen 
when  the  same  species  is  followed  into  other  localities. 
'  On  the  seaboard  it  (the  winter  change)  is  postponed 
in  comparison  with  inland  districts  in  the  same  lati- 
tudes.' In  Hudson's  Bay  Territory  it  changes  early 
and  carries  the  winter  coat  till  June,  while  no  change 
of  colour  takes  place  in  the  winter  in  the  southern 
parts  of  the  United  States.  An  individual  kept  in  a 
warm  barn  at  St.  John's,  New  Brunswick,  retained  the 
summer  colours. 

The  consideration  of  the  Hudson's  Bay  Lemming 
and  the  American  Hare  lead  to  the  conclusion  that  all 
species  in  which  the  northern  change  does  not  occur 
in  the  southern  individuals,  possess  the  power  of  Vari- 
able Eesemblance.  It  is  possible  that  the  change  is 
merely  contemporaneous  when  it  occurs  uniformly  in 
all  individuals  of  the  species,  and  it  is  at  any  rate 
probable  that  it  would  soon  become  so,  because  the 
extreme  complexity  of  the  mechanism  by  which  Vari- 
able Resemblance  is  brought  about  would  need  the 
constant  operation  of  natural  selection  to  keep  it  in 


9.8  THE  COLOUES  OF  ANIMALS 

a  state  of  efficiency.  This  consideration  is  better 
deferred  until  after  the  probable  nature  of  the 
mechanism  has  been  discussed. 


The  physical  cause  of  the  change  of  colour 

It  is  now  necessary  to  inquire  into  the  actual 
physical  cause  of  the  change  in  appearance.  It  has 
already  been  explained  that  the  dark  colour  depends 
upon  absorption,  while  the  whiteness  depends  upon 
scattering  of  light.  The  former  is  occasioned  by 
pigment  granules,  the  latter  by  included  gas  bubbles. 
When  the  latter  are  sufficiently  abundant,  the  hair 
becomes  white  in  spite  of  the  pigment ;  if  then  the 
gas  were  absorbed  the  dark  colour  would  be  restored.1 
It  appears  to  be  well  authenticated  that  in  certain 
cases  patches  of  human  hair  have  become  white 
during  some  nervous  attack,  again  becoming  dark  at 
its  cessation.  Such  changes  can  be  explained  by  the 
evolution  of  gas  (probably  carbon  di-oxide)  at  the  base 
of  the  hair,  and  its  subsequent  absorption  (probably 
by  some  alkaline  fluid).  It  is  therefore  probable  that 
the  nervous  system  can  so  modify  the  processes  taking 
place  in  the  cells  at  the  base  of  the  hair  as  to  cause 

1  This  explanation  only  applies  to  the  existing  dark  hairs  which 
become  white.  It  is  very  improbable  that  any  pigment  exists  in  the 
new  hairs  which  make  up  the  great  part  of  the  winter  coat.  Hence, 
in  testing  the  explanation  offered  above,  the  hairs  must  be  selected 
with  the  greatest  care,  and  the  investigation  should  be  conducted  in 
connection  with  an  experiment  like  that  of  Sir  J.  Boss  (see  pp.  94-96). 


VAEIABLE  RESEMBLANCE  IN  VERTEBRATA,   ETC.      99 

the  formation  of  gas  bubbles.  The  many  recorded 
cases  of  hair  turning  white  in  a  few  hours  as  the 
result  of  some  strong  nervous  shock  are  to  be  explained 
in  the  same  manner.  . 

That  the  change  in  the  long  autumnal  hairs  of 
Lepus  Americanus  is  due  to  the  appearance  of  large 
numbers  of  bubbles  is  rendered  probable  by  an  exami- 
nation of  Welch's  figures  and  descriptions.  He  speaks 
of  the  white  part  of  a  hair  being  much  broader  than 
the  coloured  part,  and  containing  additional  rows  of 
'cells.'  His  'cells'  appear  to  be  bubbles  of  gas, 
and  he  draws  them  with  the  characteristic  dark 
borders.  It  must  be  remembered  that  the  dark  parts 
of  a  hair  also  contain  bubbles,  although  in  smaller 
amount. 


The  change  in  the  hair  is  indirectly  caused  by  the 
change  of  temperature 

It  is  extremely  improbable  (to  say  the  least)  that 
such  changes  as  the  evolution  of  bubbles,  and  above 
all,  the  growth  in  length,  are  the  direct  result  of  a 
lowered  temperature  on  the  hair  itself.  That  they 
are  indirect  results,  through  the  nervous  system,  is  in 
every  way  probable,  and  is  furthermore  in  harmony 
with  certain  well-known  facts  concerning  the  regula- 
tion of  temperature. 

The  direct  tendency  of  cold  is  clearly  to  diminish 
the  activity  of  those  processes  upon  which  the  pro- 


100  THE  COLOUKS  OF  ANIMALS 

duction  of  heat  depends,  just  as  it  would  tend  to 
dimmish  rather  than  promote  the  growth  of  hair. 
This  direct  effect  is  obvious  in  animals  which  are  un- 
injured by  variations  of  temperature.  '  The  body  of 
a  cold-blooded  animal  behaves  in  this  respect  like  a 
mixture  of  dead  substances  in  a  chemist's  retort : 
heat  promotes  and  cold  retards  chemical  action  in 
both  cases.'  But  the  higher  vertebrates  are  warm- 
blooded (homothermic),  and  such  direct  effects  of  cold 
would  be  fatal.  '  In  these  animals  there  is  obviously 
a  mechanism  of  some  kind  counteracting,  and  indeed 
overcoming,  those  more  direct  effects  which  alone 
obtain  in  cold-blooded  animals.'  The  influence  of 
cold  upon  the  nerves  of  the  skin  constitutes  a  stimulus 
to  that  part  of  the  central  nervous  system  which 
regulates  the  production  of  heat :  thus  cold  indirectly 
increases  the  amount  of  heat,  and  the  temperature 
of  the  body  remains  constant.  I  may  mention  that 
the  amount  of  heat  produced  in  the  body  at  any  one 
time  may  be  gauged  by  the  amount  of  oxygen  ab- 
sorbed in  respiration.1 

It  is  in  every  way  probable  that  such  changes  in 
colour  as  that  of  Sir  J.  Boss'  Lemming  and  the 
American  Hare  are  also  indirectly  caused  by  the  cold, 
which  we  may  suppose  acts  as  a  stimulus  to  that  part 

1  For  a  further  account  of  the  regulation  of  temperature  see 
Professor  MichaeT  Foster's  Physiology,  from  which  the  quoted 
sentences  are  taken.  I  owe  the  correct  understanding  of  the  physical 
cause  of  the  change  of  colour  to  a  conversation  with  Professor 
Foster. 


VAEIABLE  KESEMBLANCE  IN  VERTEBEATA,  ETC.      101 

of  the  nervous  system  which  presides  over  the  nu- 
tritive and  chemical  changes  involved  in  the  growth 
of  hair  and  the  appearance  of  the  bubbles. 


Probable  variation  in  susceptibility  to  stimulus  of 
cold  in  different  districts 

In  the  northern  part  of  an  animal's  range,  natural 
selection  would  favour  great  delicacy  in  the  adjustment 
of  the  mechanism  by  which  such  changes  are  produced, 
so  that  the  winter  coat  would  be  ready  in  time  to 
harmonise  with  the  mantle  of  snow.  Conversely, 
extreme  delicacy  would  be  a  disadvantage  in  the 
southern  part  of  the  range,  if  the  climate  were  such 
that  the  snow  did  not  lie  on  the  ground  for  any  great 
part  of  the  winter.  There  is  abundant  evidence  of 
variations  in  the  delicacy  of  adjustment,  upon  which 
natural  selection  could  operate. 

Mr.  F.  E.  Beddard  has  directed  my  attention  to 
three  Arctic  Foxes  (Cam's  lagopus)  from  Iceland,  which 
have  been  in  the  Zoological  Gardens  since  1887. 
One l  of  these  turns  perfectly  white  every  winter,  while 
the  other  two  remain  dark. 

The  stoat  always  becomes  white  in  the  alpine 
districts  of  Scotland,'  frequently  in  the  north  of  Eng- 

1  When  I  examined  this  fox  on  October  14,  1889,  the  change  in 
colour  was  nearly  complete  :  there  was,  however,  a  grey  patch  of  hair 
on  the  back  which  was  certainly  moulting.  It  is  possible,  therefore, 
that  the  change  is  effected  in  an  entirely  different  manner  in  this 
species. 

6 


102         THE  COLOURS  OF  ANIMALS 

land,  occasionally  in  the  Midlands,  and  Mr.  Couch 
has  seen  two  white  stoats  in  Cornwall.1  It  would  be 
extremely  interesting  to  take  a  number  of  Scotch 
stoats  to  Cornwall  and  an  equal  number  of  Cornish 
stoats  to  Scotland,  in  order  to  test  whether  the 
southern  individuals  are  less  susceptible  to  change 
than  the  northern.  It  is  likely  that  the  great  differ- 
ence is  not  wholly  to  be  explained  by  the  relation  of 
northern  to  southern  temperature,  but  at  any  rate 
partially  by  the  fact  that  the  change  is  disadvantageous 
in  most  parts  of  England ;  for  it  would  render  the 
animal  conspicuous  against  the  prevalent  tints  of  a 
midland  or  southern  winter.  Of  course,  any  such 
disadvantage  implies  that  natural  selection  would 
gradually  blunt  the  susceptibility  of  the  apparatus  by 
which  the  change  is  produced.  The  rare  cases  of 
a  change  of  colour  in  Cornwall  are  probably  examples 
of  a  formerly  beneficial  susceptibility,  as  yet  unaltered 
by  natural  selection. 

Loss  pf  susceptibility  to  stimulus  of  cold  in  animals 
which  remain  white  all  the  year 

Such  a  nervous  mechanism  as  that  to  which  I  have 
alluded,  would  be  of  the  highest  intricacy  and  com- 
plexity, and  would  speedily  lose  its  efficiency  unless 
constantly  preserved  by  natural  selection.  Thus 
certain  Arctic  animals  which  remain  on  the  snow 

1  Boll :  British  Quadrupeds,  second  edition,  pp.  196-201. 


VAEIABLE  RESEMBLANCE  IN  VEETEBEATA,  ETC.      103 

nearly  all  the  year  retain  the  white  coat  permanently, 
and  there  is  no  need  for  the  mechanism  by  which  the 
change  is  produced.  And  yet  in  certain  species  we 
may  feel  sure  that  such  a  mechanism  existed  under 
former  conditions.  Thus  the  Arctic  Hare  (Lepus 
glacialis)  usually  remains  white  all  the  summer ;  oc- 
casionally, however,  it  becomes  greyish,  the  change 
of  colour  being  limited  to  the  points  of  the  hair : 
the  young  are  born  grey,  but  change  to  white  at 
their  first  winter  (Welch).  The  latter  change 
appears  to  be  independent  of  cold,  for  Sir  J.  Boss 
speaks  of  a  young  hare  turning  white  as  early  as 
those  running  wild,  although  in  a  temperature  not 
much  below  freezing.  This  observation  forms  an  in- 
teresting contrast  with  the  behaviour  of  species  pos- 
sessing an  efficient  nervous  mechanism  (the  Hudson's 
Bay  Lemming  and  the  American  Hare)  when  shielded 
from  a  low  temperature. 


The  white  winter  coat  chiefly  for  concealment,  but 
may  also  help  to  retain  heat 

Certain  northern  animals,  especially  those  fre- 
quenting trees,  do  not  become  white  in  winter :  this 
is  true  of  the  Glutton  (Gulo  luscus).  Occasionally 
dark  winter  individuals  occur  in  species  which  as  a 
rule  change  their  colour  regularly :  thus,  a  black 
Arctic  Fox  is  well  known,  but  its  rarity  (Sir  J.  Eoss 
found  three  individuals  out  of  fifty  white  ones)  prob- 


104  THE  COLOTJKS  OF  ANIMALS 

ably  indicates  that  it  is,  as  we  should  expect,  at  a 
disadvantage,  and  that  it  will  disappear.  Mr.  Wallace 
considers  that  the  dark  colour  of  arboreal  northern 
animals,  which  is  clearly  for  concealment,  disproves 
the  theory  that  the  white  colour  is  of  value  in  retain- 
ing animal  heat.  But  it  does  not  follow  that  such 
benefits  are  wholly  non-existent,  because  they  must 
be  dispensed  with  under  the  pressure  of  a  stronger 
necessity.  Mr.  Wallace's  argument  shows  that  con- 
cealment is  the  paramount  necessity ;  but  this  does 
not  disprove  the  opinion  that  other  advantages  also 
may  be  conferred  by  one  particular  mode  in  which 
concealment  is  attained. 


The  seasonal  change  of  colour  in  northern  birds 

The  same  convincing  evidence  as  to  the  nature  of 
the  .change,  and  the  manner  in  which  it  is  brought 
about,  has  not  yet  been  brought  forward  hi  the  case 
of  birds.  Mr.  A.  H.  Cocks,  who  has  had  a  very  wide 
experience  of  northern  animals,  believes  that  it  is  at 
least  partially  due  to  a  change  in  the  autumnal 
feathers.  He  writes :  '  I  have  some  specimens  of 
Lagopus  (various  species)  showing  brown  feathers 
with  white  tips,  and  in  one  species,  at  any  rate,  the 
converse.'  Mr.  E.  Bowdler  Sharpe  does  not  however 
think  that  the  evidence  of  a  winter  change  in  existing 
feathers  is  sufficient.1  He  has  nevertheless  proved 

1  H.  Seebohm  thinks  it  '  possible  that  the  white  winter  feathers 


VAEIABLE  KESEMELANCE  IN  VERTEBRATA,  ETC.      105 

that  other  changes  of  colour  do  occur,  as  will  be  seen 
in  the  following  passage  from  his  most  interesting 
paper.1 

'  Let  any  one  who  doubts  the  possibility  of  mark- 
ings such  as  those  on  the  Greenland  Falcon  becoming 
gradually  changed  without  an  intermediate  moult, 
study  the  changes  exhibited  by  the  common  Sparrow 
Hawk  in  its  progress  towards  maturity.  The  general 
characteristic  of  the  species  of  Accipiter  is  to  have  a 


striped  plumage  when  young  and  a  barred  dress  when 
old.  But  it  is  not-  generally  known  that  this  is 
effected  by  a  gradual  change  in  the  markings  of  the 
feather,  and  not  by  an  actual  moult.  On  the  first 
appearance  of  the  feathers  from  the  downy  covering 
of  the  nestling,  the  markings  on  the  chest  are  longi- 
tudinal drops  (fig.  18)  of  a  pale  rufous-brown  colour. 
The  gradual  dissolution  and  breaking  up  into  three 
bars  is  shown  in  fig.  19.  Hence,  when  the  bars  are 
perfectly  developed  a  shade  of  darker  brown  over- 

(of  Ptarmigan)  gradually  change  colour  in  spring,  only  those  being 
moulted  which  have  been  injured  in  winter.'— British  Birds,  vol.  ii. 
p.  427,  n. 

1  Proc.  Zool.  Spc.  1873,  pp.  414  et  sec[. 


106         THE  COLOUES  OF  ANIMALS 

spreads  the  upper  margin,  gradually  eclipsing  the 
rufous-brown  shade,  which  remains  the  evidence  of 
the  previous  plumage  (fig.  20).  Hence  are  shown 
two  successive  stages  of  the  development  of  the  dark 
brown  shade  which  at  last  removes  all  traces  of  the 
reddish  tint  (figs.  21  and  22).' 

If  the  winter  change  does  not  occur  in  the 
autumnal  feathers,  it  by  no  means  follows  that 
the  power  of  Variable  Eesemblance  is  absent.  The 
growth  of  new  white  feathers  may  be  indirectly  due 


to  the  cold,  acting  through  the  medium  of  the  nervous 
system.  This  is,  however,  very  far  from  being  proved ; 
for  it  does  not  appear  to  be  certain  that  there  is  a 
single  species  becoming  white  in  winter  which  retains 
its  dark  colour  at  this  time  of  the  year  in  the  southern- 
most part  of  its  range. 

Mr.  A.  C.  Billups,  of  Niagara,  Ontario,  tells  me 
that  during  an  exceptionally  mild  winter,  about 
seven  or  eight  years  ago,  neither  the  '  snow  bird ' 
nor  the  American  Hare  acquired  the  winter  dress. 
Hence  the  power  of  Variable  Resemblance  appears  to 
be  possessed  by  certain  birda. 


VAEIABLE  EESEMBLANCE  IN   VERTEBKATA,  ETC.      107 


Variable  Resemblance  of  northern  animals  most  nearly 
related  to  that  of  certain  insects 

The  acquisition  of  a  special  winter  covering  as  a 
response  to  the  stimulus  of  cold  is  most  nearly  related 
to  the  Variable  Eesemblance  exhibited  by  many  cater- 
pillars and  chrysalides.  It  will  be  shown  in  the  next 
chapter  that  these  latter  changes  are  similar  to  the 
above  in  that  the  stimulus  (of  reflected  light)  acts 
upon  the  skin ;  that  the  results  are  in  all  probability 
indirect,  and  take  place  through  the  part  of  the 
nervous  system  which  regulates  the  production  of 
colour ;  finally,  that  far  greater  time  is  required  for 
the  accomplishment  of  the  change  than  in  those 
animals  in  which  the  stimulus  acts  upon  the  eye,  and 
in  which  existing  pigments  are  arranged  instead  of  new 
substances  elaborated. 


Rapid  adjustment  of  Colour  in  certain  invertebrate 
animals 

Certain  invertebrate  animals,  however,  possess  the 
power  of  rapidly  adjusting  their  colour  to  that  of  their 
surroundings.  It  is  well-known  in  Crustacea,  and  is 
probably  very  common  among  them.  The  power  has 
been  proved  to  depend  upon  the  eye  as  among  the 
vertebrates.  Some  cuttle-fish  also  can  modify  their 
colours  in  the  same  manner,  with  remarkable  pre- 


108  THE  COLOURS  OF  ANIMALS 

cision  and  rapidity.  The  resemblance  between 
certain  individuals  of  Ovulum  and  the  rose-coloured 
coral,  and  between  other  individuals  and  the  yellow 
coral  (see  pp.  70-71),  is  probably  due  to  the  existence 
of  a  power  of  adjustment ;  but  this  suggestion  needs 
experimental  verification.  A  fact  mentioned  by  Morse 
is  even  more  convincing :  he  states  that  individuals 
of  the  same  molluscan  species  occupying  different 
stations  are  differently  coloured,  and  he  quotes  from 
Dr.  A.  A.  Gould  the  observation  that  the  colour  of  all 
the  shells  found  in  the  sandy  harbour  of  Provincetown 
is  remarkably  light.1  There  is  no  evidence  as  to 
whether  the  change  in  colour,  if  produced  at  all,  takes 
place  rapidly  or  slowly ;  but  the  latter  is  the  more 
probable  in  these  animals. 

Professor  Stewart  found  four  or  five  bright  red 
individuals  of  the  Nudibranchiate  mollusc  Archidoris 
tuberculata  in  a  mass  of  bright  red  sponge  (Hymenia- 
cidon  sanguined)  upon  which  they  were  feeding.2 
The  colour  was  very  different  from  that  of  individuals 
taken  upon  another  sponge  (Halichondria) .  The  ob- 
servation strongly  suggests  the  existence  of  a  power  of 
Variable  Protective  Eesemblance,  although  it  is  possible 
that  the  colour  of  the  food  may  be  made  use  of. 

It  is  very  likely  that  Variable  Eesemblance  will 
be  found  to  occur  far  more  generally  than  has  been 
hitherto  supposed. 

1  Proc.  Boston  Soc.  Nat.  Hist.  vol.  xiv.  April  5,  1871. 

2  W.  Garstang,  l.c.  p.  177. 


VARIABLE  RESEMBLANCE  IN  VERTEBRATA,  ETC.      109 


Variable  Resemblance,  Protective  and  Aggressive 

As  in  so  many  other  cases,  the  specialised  form  of 
concealment  by  the  organism  resembling  its  surround- 
ings treated  of  in  this  chapter  may  be  either  Protective 
or  Aggressive ;  it  may  enable  an  animal  to  escape  its 
enemies  or  to  approach  its  prey  unseen.  Frequently 
it  may  be  turned  to  both  uses  by  a  single  animal. 
Thus  the  green  tree  frog  is  probably  aided  in  cap- 
turing the  insects  on  which  it  feeds  because  of  its 
close  resemblance  to  the  leaves  around  it ;  but  it  is 
also  protected  in  the  same  manner  from  the  animals 
which  prey  upon  it.  Thus  Mr.  E.  A.  Minchin  tells 
me,  from  his  experience  in  India,  that  tree  frogs  are 
sought  for  with  especial  eagerness  by  snakes,  which 
greatly  prefer  them  to  others.  It  is  probable  that 
this  power  when  possessed  by  a  vertebrate  animal 
nearly  always  bears  a  double  meaning,  although  a  con- 
sideration of  the  different  instances  will  show  that  it 
is  especially  Protective  in  some  and  especially  Aggres- 
sive in  others.  In  the  next  chapter  we  shall  meet 
with  a  large  number  of  cases  briefly  alluded  to  at  the 
beginning  of  this  chapter,  in  which  the  power  is  in 
many  respects  different,  and  possesses  an  entirely 
Protective  meaning. 


110         THE  COLOUES  OF  ANIMALS 


CHAPTEE  VIII 

VARIABLE  PROTECTIVE   RESEMBLANCE   IN 
INSECTS 

No  insect  is  known  to  possess  the  power  of  rapidly 
adjusting  its  colour  to  the  tints  of  its  surroundings, 
and  it  has  not  long  been  known  that  any  power  of 
adjustment  exists.  There  is  still  a  great  deal  to  be 
done  in  finding  out  the  extent  to  which  the  power  is 
present,  and  in  further  investigating  the  physiological 
processes  which  are  involved  in  its  operation.  Up  to 
the  present  time  the  Lepidoptera  (butterflies  and 
moths)  alone  have  been  made  the  subjects  of  in- 
quiry, and  we  know  nothing  of  other  insects  in  this 
respect. 

Many  caterpillars  and  chrysalides  have  been  proved 
to  be  capable  of  adjusting  their  colours  to  those  of  the 
surroundings,  and  it  is  also  known  that  certain  cater- 
pillars can  construct  cocoons  of  different  colours,  so 
as  to  harmonise  with  the  environment.  The  latter 
extremely  interesting  example  of  Variable  Protective 
Resemblance  has  been  very  insufficiently  investigated. 
It  is  also  probable  that  a  relatively  small  number  of  per- 
fect insects  possess  the  same  power  ;  but  in  this  case 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS     111 

no  experimental  researches  have  been  conducted.  I 
will  first  consider  the  chrysalides,  because  they  were 
first  found  to  possess  the  power,  and  because  it  has 
been  more  completely  investigated  in  them  than  in 
the  other  cases. 


Variable  Protective  Eesemoiance  in  Lepidopterous  Pupae. 

The  capability  of  adjusting  the  colour  to  that 
of  the  surroundings  is  only  present  in  exposed  chry- 
salides, and  has  not  been  found  hitherto  among 
the  pupae  of  Heterocera  (or  moths),  nearly  all  of 
which  are  either  buried  in  the  earth  or  concealed  in 
opaque  cocoons.  In  both  cases  the  chrysalides  are 
generally  reddish-brown  hi  colour,  the  shade  varying 
greatly  in  different  species.  The  dark  colour  is  of  pro- 


FIG.  23. — The  pupa  of  Swallow-  FIG.  24. — The  pupa  of  Swallow- 
tailed  Moth,  showing  colour  tailed  Moth  (Uropteryx  sambu- 
assuined  when  the  larva  has  caia) ;  the  usual  dark  colour 
been  placed  on  white  paper  assumed  in  cocoon ;  natural 
before  pupation.  size. 

tective  value  when  the  chrysalis  is  accidentally  ex- 
posed upon  the  surface  of  the  earth. 

Since  this  last  paragraph  was  written,  I  have 
found  that  the  chrysalis  of  the  Swallow-tailed  Moth 


112         THE  COLOURS  OF  ANIMALS 

(Uropteryx  samlwcata)  becomes  light-coloured  when 
the  caterpillar  has  been  placed  upon  white  paper 
shortly  before  pupation  (see  fig.  23).  The  chrysalis 
is  usually  dark  (see  fig.  24),  and  is  contained  in  a 
cocoon  which  is  formed  of  the  brown  fragments  of 
leaves  or  twigs  spun  together  with  threads  of  silk. 
The  cocoon,  which  is  suspended  from  the  food-plant 
and  swings  freely,  is  so  loose  and  open  in  texture  that 
the  enclosed  pupa  is  easily  seen,  and  is  in  fact  as 
exposed  as  that  of  many  butterflies. 

The  chrysalides  of  butterflies  are  generally  freely 
exposed,  and  many  species  have  been  proved  to  possess 
the  power  of  adjusting  the  pupal  colour  to  that  of 
the  adjacent  surface.  Such  pupse  are  often  suspended 
head  downwards  from  a  boss  of  silk,  to  which  the 
hooks  at  the  posterior  end  are  affixed ;  or  they  are  fre- 
quently attached  horizontally,  or  in  a  vertical  position 
with  the  head  upwards,  by  similar  posterior  hooks  and 
a  strong  silken  girdle,  which  is  fixed  on  either  side  to 
the  supporting  surface,  and  which  sinks  into  a  groove 
across  the  back  of  the  pupa.  The  group  which  in- 
cludes the  Tortoiseshell  and  Peacock  Butterflies  adopts 
the  former  mode  of  suspension;  that  to  which  the 
*  Garden  Whites  '  belong  adopts  the  latter. 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    1 13 


The  History  of  the  Discovery  of  Variable  Protective 
Resemblance  in  the  pupae  of  Butterflies 

In  1867  Mr.  T.  W.  Wood  exhibited  to  the  Entomo- 
logical Society  of  London  l  a  number  of  chrysalides  of 
the  Swallow-tailed  Butterfly  (Papilio  machaori),  and  of 
the  large  and  small  Garden  White  Butterflies  (Pieris 
brassicce  and  P.  rapes),  which  corresponded  in  colour  to 
the  surfaces  to  which  they  were  attached.  Dark 
pupse  had  been  found  on  tarred  fences  and  in  subdued 
light ;  light  ones  on  light  surfaces ;  while  green  leaves 
were  shown  to  produce  green  chrysalides,  at  any  rate 
in  certain  cases.  Mr.  Wood's  inclusion  of  the  chrysalis 
of  the  Swallow-tail,  with  which  he  states  that  he  was 
imperfectly  acquainted,  was  most  unfortunate,  and 
doubtless  prevented  his  suggestive  paper  from  gaining 
the  success  it  deserved.  It  is  quite  true  that  this 
chrysalis  appears  in  two  forms,  being  sometimes  green 
and  sometimes  dark  grey ;  but,  without  sufficient  evi- 
dence, it  was  unwise,  although  most  natural,  to  assume 
that  these  colours  could  be  adjusted  to  green  or  dark 
surroundings  respectively.  I  have  since  tested  the 
chrysalis,  and  as  far  as  my  experiments  (which  were 
with  small  numbers)  are  conclusive,  they  show  that  it 
has  no  power  of  adjustment.2  In  the  discussion  which 
followed  Mr.  Wood's  paper,  Mr.  Bond  stated  that  '  he 

1  Proc.  Ent.  Soc.  1867,  pp.  xcix.-ci. 

•  Phil.  Trans  vol.  178  (1887),  B.  p.  406-408. 


114  THE  COLOURS  OF  ANIMALS 

had  had  thousands  of  pupae  of  Papilio  machaon,  and 
had  often  had  the  brown  variety  of  pupa  on  a  green 
ground  colour,  whilst  in  some  seasons  he  had  obtained 
no  brown  specimens  at  all.' 

In  spite  of  this  unfortunate  mistake,  Mr.  Wood 
adduced  quite  sufficient  evidence  concerning  the 
Garden  Whites  to  show  that  the  subject  was  worth 
investigation.  But  the  great  example  and  the  great 
principles  of  Darwin  had  not  penetrated  far  into  the 
mass  of  naturalists ;  and  distinguished  entomologists 
preferred  the  expression  of  an  adverse  opinion,  to 
making  an  easy  experiment  upon  one  of  our  commonest 
insects. 

Mr.  Wood  also  stated  that  the  chrysalis  of  the 
Large  Tortoiseshell  Butterfly  (Vanessa  polychloros)  was 
coloured  like  a  withered  elm-leaf,  when  suspended 
among  the  foliage  of  the  elm  on  which  its  caterpillar 
feeds.  Its  colour  was  then  light  reddish-brown  with  a 
cluster  of  metallic  silvery  spots,  but  when  suspended 
from  a  wall,  the  metallic  spots  were  not  produced, 
and  the  pupa  was  of  a  mottled  greyish  colour.  This 
observation  led  Mr.  Wood  to  conclude  '  that  by  the 
proper  use  of  gilded  surfaces  the  gilded  chrysalides  of 
Vanessa,  and  perhaps  of  other  genera,  would  be  ob- 
tained ' ;  and  he  added,  '  I  hope  to  be  able  to  try  the 
experiment  next  season.'  If  this  intention  had  been 
carried  out,  such  startling  results  would  have  been 
obtained  that  opposition  would  have  broken  down 
before  them,  and  the  combined  researches  of  many 


VAEIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    115 


naturalists  would  have  been  brought  to  bear  upon  the 
subject.  The  experiment,  however,  was  not  made  till 
nineteen  years  later,  when  I  was  led  to  do  as  Mr. 
Wood  had  proposed,  although  unaware  at  the  time  of 
his  suggestion. 

Nevertheless,  during  these  nineteen  years,  gradual 
confirmation  of  Mr.  Wood's  central  position  was 
afforded.  In  1873  Professor  Meldola  supported  the 
observations  upon  the  chrysalides  of  the  '  Garden 
Whites.'  He  compared  large 
numbers  of  individuals,  and 
found  that  the  pupse  upon 
black  fences  were  darker 
than  those  upon  walls.1 

In  1874  a  paper  by  Mrs. 
M.  E.  Barber,  and  commu- 
nicated by  Mr.  Darwin  to 
the  Entomological  Society 
of  London,  was  printed  in 
the  Transactions  of  that 
society.2  'Mrs.  Barber  had 
experimented  with  a  com- 
mon South  African  Swallow- 
tailed  Butterfly  (Papilio 
nireus),  and  had  found  the 
chrysalis  wonderfully  sensi- 
tive to  the  colours  of  its  environment.  When  the 
pupae  were  attached  among  the  deep  green  leaves  of 

1  Zool.  Soc.  Proc.  1873,  p.  153.  2  1874,  p.  519. 


FIG.  25.— The  pnpa  of  Papttio  nireus 
attached  to  orange  tree ;  natural 


116 


THE  COLOUES  OF  ANIMALS 


the  food-plant,  Orange,  they  were  of  a  similar  colour 
(see  fig.  25) ;  when  fixed  to  dead  branches  covered 
with  withered,  pale  yellowish-green  leaves,  they  re- 
sembled the  latter  (see  fig.  26).  One  of  the  cater- 
pillars '  affixed  itself  to  the  wooden  frame  of  the  case, 


FIG.  26.— The  pupa  of  PapHio  niretu 
attached  to  plant  (Veprii  lanceo- 
lata)  with  withered  yellowish-green 


7. — The  pupa  of  Papilio  nireus 
attached  to  woodwork. 


and  then  became  a  yellowish  pupa  of  the  same  colour 
as  the  wooden  frame'  (see  fig.  27).  The  case  was 
made  partly  of  purplish-brown  brick  and  partly  of 
wood,  and  one  of  the  pupae,  attached  close  to  the 
junction,  was  believed  by  Mrs.  Barber  to  have  assumed 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    117 

both  colours,  that  of  the  brick  upon  its  back  and  that 
of  the  wood  upon  its  under  surface.  My  experiments 
upon  the  chrysalis  of  the  Small  Tortoiseshell  Butterfly, 
to  be  described  below,  do  not  support  this  conclusion, 
and  it  is  a  common  thing  for  the  colours  of  pupae  to 
differ  greatly  in  the  dorsal  and  ventral  regions.  Mrs. 
Barber  also  tried  the  effect  of  scarlet  cloth,  but  little 
if  any  influence  was  exerted. 

Mr.  Mansel  Weale  also  showed  that  the  colour  of 
certain  other  South  African  pupae  can  be  modified,1 
and  Mr.  Roland  Trimen  made  some  experiments 
upon  another  African  Swallow-tail 2  (Papilio  demoleus, 
common  at  Cape  Town),  confirmatory  of  Mrs.  Barber's 
observations.  He  covered  the  sides  of  the  cage  with 
bands  of  many  colours,  and  found  that  green,  yellow, 
and  reddish-brown  tints  were  resembled  by  the  pupae, 
while  black  made  them  rather  darker.  Bright  red 
and  blue  had  no  effect.  The  larvae  did  not  exercise 
any  choice,  but  fixed  themselves  indiscriminately  to 
colours  which  their  pupae  could  resemble  and  those 
which  they  could  not.  In  the  natural  condition  the 
latter  would  not  exist,  for  the  pupae  can  imitate  all 
the  colours  of  their  normal  environments. 

Finally,  Fritz  Miiller  experimented  upon  a  South 
American  Swallow-tail  (Papilio  poly  damns)?  and  found 


Trans.  Ent.  Soc.  Land.  1877,  pp.  271,  275. 
2  Described  in  a  letter  to  me,  published  in  my  paper  already 
referred  to,  p.  316. 

*  Eosmos,  vol.  12,  p.  448. 


118         THE  COLOURS  OF  ANIMALS 

that  its  pupae,  although  appearing  in  two  forms,  dark 
and  green,  like  those  of  our  own  Swallow-tail,  also 
resemble  the  latter  in  having  no  power  of  adjusting 
their  colours  to  the  surroundings. 


Theories  as  to  the  manner  in  which  the  colours  of  such 
pupae  are  determined 

These  observations  and  experiments  had  been 
made  when  I  began  to  work  at  the  subject  in  1886  : 
they  appeared  to  prove  that  the  power  certainly  exists, 
but  nothing  was  really  known  as  to  the  manner  in 
which  the  adjustment  is  effected.  Mr.  T.  W.  Wood's 
original  suggestion,  that  'the  skin  of  the  pupa  is 
photographically  sensitive  for  a  few  hours  only  after 
the  caterpillar's  skin  has  been  shed,'  was  accepted 
by  most  of  those  who  had  worked  at  the  subject. 
And  yet  the  suggestion  rested  upon  no  shadow  of 
proof ;  it  depended  upon  a  tempting  but  overstrained 
analogy  to  the  darkening  of  the  sensitive  photographic 
plate  under  the  action  of  light.  But  the  analogy 
was  unreal,  for,  as  Professor  Meldola  stated  in  the 
discussion  which  followed  Mrs.  Barber's  paper,  '  the 
action  of  light  upon  the  sensitive  skin  of  a  pupa 
has  no  analogy  with  its  action  on  any  known  photo- 
graphic chemical.  No  known  substance  retains  per- 
manently the  colour  reflected  on  it  by  adjacent 
objects.'  The  supposed  '  photographic  sensitiveness ' 
of  chrysalides  was  one  of  those  deceptively  feasible  sug- 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   119 

gestions  which  are  not  tested  because  of  their  apparent 
probability.  It  would  have  been  very  easy  to  transfer 
a  freshly  formed  pupa  from  one  colour  to  another 
which  is  known  to  produce  an  opposite  effect  upon  it ; 
and  yet  if  this  simple  experiment  had  been  made  the 
theory  would  have  collapsed,  for  the  pupa  would  have 
been  found  to  resemble  the  first  colour  and  not  the 
second.  Furthermore,  Mr.  Wood's  suggestion  raised 
the  difficulty  that  chrysalides  which  had  become  ex- 
posed in  the  course  of  a  dark  night  would  have  no 
opportunity  of  resembling  the  surrounding  surfaces, 
for  the  pupal  colours  deepen  very  quickly  into  their 
permanent  condition.  In  working  at  the  subject  I 
determined  to  pay  especial  attention  to  such  ques- 
tions. 

Experiments  upon  the  chrysalis  of  the  Peacock 
Butterfly 

I  began  work  with  the  common  Peacock  Butterfly 
(Vanessa  lo),  of  which  the  chrysalis  appears  in  two 
forms,  being  commonly  dark  grey  (see  fig.  28),  but 
more  rarely,  bright  yellowish-green  (see  fig.  29) :  both 
forms  are  gilded,  especially  the  latter.  The  gilding 
cannot  be  represented  in  the  woodcuts.  Only  six 
caterpillars  could  be  obtained,  and  these  were  placed 
in  glass  cylinders  surrounded  by  yellowish-green 
tissue  paper.  Five  of  them  became  chrysalides  of  the 
corresponding  colour;  the  sixth  was  removed  imme- 
diately after  the  caterpillar  skin  had  been  thrown 


120        THE  COLOUES  OF  ANIMALS 

off,  and  was  placed  in  a  dark  box  lined  with  black 
paper,   but  it   subsequently  deepened  into  a  green 


PIG.  28.— The  pupa  of  Peacock  FIG.   29.— The  pupa  of  Peacock 

Butterfly  ;  dark  form ;  natural  Butterfly ;  light  yellowish-green 

size.  form. 

pupa  exactly  like  the  others.  Obviously  the  sur- 
roundings had  exercised  their  influence  before  the 
pupa  was  removed. 


Experiments  upon  the  chrysalis  of  the  Small  Tortoise- 
shell  Butterfly 

Being  unable  to  obtain  more  larvae  of  the  Peacock, 
I  worked  upon  the  allied  Small  Tortoiseshell  Butterfly 
(Vanessa  urticce),  which  can  be  obtained  in  immense 
numbers.  In  the  experiments  conducted  in  1886, 
over  700  chrysalides  of  this  species  were  obtained  and 
their  colours  recorded.  Green  surroundings  were 
first  employed  in  the  hope  that  a  green  form  of  pupa, 
unknown  in  the  natural  state,  might  be  obtained. 
The  results  were,  however,  highly  irregular,  and  there 
seemed  to  be  no  susceptibility  to  the  colour.  The  pupas 
were,  however,  somewhat  darker  than  usual,  and  this 


VAEIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    121 

result  suggested  a  trial  of  black  surroundings,  from 
which  the  strongest  effects  were  at  once  witnessed : 
the  pupae  were  as  a  rule  extremely  dark,  with  only 
the  smallest  trace,  and  often  no  trace  at  all,  of  the 
golden  spots  which  are  so  conspicuous  in  the  lighter 
forms.  These  results  suggested  the  use  of  white  sur- 
roundings, which  appeared  likely  to  produce  the  most 
opposite  effects.  The  colours  of  nearly  150  chrysalides 
obtained  under  such  conditions  were  very  surprising. 
Not  only  was  the  black  colouring  matter  as  a  rule 
absent,  so  that  the  pupae  were  light-coloured,  but 
there  was  often  an  immense  development  of  the 
golden  spots,  so  that  in  many  cases  the  whole  surface 
of  the  pupae  glittered  with  an  apparent  metallic  lustre. 
So  remarkable  was  the  appearance  that  a  physicist,  to 
whom  I  showed  the  chrysalides,  suggested  that  I  had 
played  him  a  trick  and  had  covered  them  with  gold-leaf. 

These  remarkable  results  led  to  the  use  of  a  gilt 
background  as  even  more  likely  to  produce  and  in- 
tensify the  glittering  appearance.  By  this  reasoning 
I  was  led  to  make  the  experiment  which  had  been 
suggested  by  Mr.  Wood  nineteen  years  before.  The 
results  quite  justified  the  reasoning,  for  a  much  higher 
percentage  of  gilded  chrysalides,  and  still  more  remark- 
able individual  instances,  were  obtained  among  the 
pupae  which  were  treated  in  this  way. 

The  following  table  shows  the  results  of  some  ex- 
periments in  which  the  above-mentioned  colours  were 
employed : — 


122 


THE  COLOUKS   OF  ANIMALS 


Dark 

Light 

(1) 

(2) 

(3) 

(3) 

(3) 

(4) 

(5) 

•„->> 

i| 

'L 

If 

g2-3 

a| 

| 

Degrees  of  colour 

*% 

•8-S 

*£ 

-  g  -Si 

^  g-§ 

""  0 

s  ? 

I  js"S 

11 

ii 

0  '-£ 

*!^ 

,§» 

slS 

.£fS  « 

|g 

"il 

"£>„„ 

S^« 

£  1 

||| 

0  c3 

•all 

&1| 

al 

H 

3 

o" 

SKI 

guw 

t> 

Totals 

Green  surroundings 
Black 

2 
11 

8 
29 

27 

25 
22 

14 

1 
2 

8 

=   3 

=  105 

White 

— 

7 

21 

37 

44 

25 

11 

=  145 

Gilt             „ 

— 

1 

2 

7 

16 

27 

14 

-  67 

356 

In  order  to  realise  these  results  it  must  be  remembered 
that  the  appearance  represented  by  (4)  or  (5)  is  very 
rarely  seen  in  nature,  except  when  the  pupa  is  dis- 
eased. By  far  the  commonest  varieties  met  with  are 
those  represented  by  (3),  which  are  therefore  called 
normal  forms. 


Special  advantages  of  the  Small  Tortoiseshell  for 
purposes  of  experiment 

From  the  results  expressed  in  the  tabular  form 
given  above,  it  was  clear  that  this  species  was  very 
susceptible  to  surrounding  colours,  and  that  black 
and  gold  produced  the  most  opposite  effects.  Another 
advantage  in  the  use  of  this  species  is  the  fact  that 
the  caterpillars  live  in  companies,  each  of  which 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    123 

develops  from  the  eggs  laid  by  a  single  butterfly. 
Hence  by  keeping  the  companies  separate,  the  varying 
hereditary  tendencies,  due  to  different  parentage,  are 
eliminated ;  for  a  company  of  moderate  size  would 
contain  over  one  hundred  larvae,  and  would  therefore 
furnish  the  material  for  several  experiments.  Con- 
sidering also  the  abtuadance  of  the  species,  I  determined 
to  employ  it  for  the  investigation  of  the  process  by 
which  the  change  of  colour  is  effected. 

The  pupae  darker  when  crowded  together 

Very  early  in  the  investigation  a  possible  source 
of  error  was  detected.  It  seemed  probable,  when 
many  individuals  were  collected  together  at  the  sus- 
ceptible period,  which  will  be  shown  to  occur  towards 
the  end  of  larval  life,  that  each  of  them  would  be 
affected  by  that  part  of  the  surroundings  which  was 
constituted  by  the  black  skins  of  its  neighbours.  It 
was  therefore  necessary  to  take  into  account  the 
relative  positions  of  the  pupae,  and,  in  the  most 
careful  experiments,  to  place  only  a  single  individual 
in  each  coloured  case.  Experiment  soon  showed 
that  these  precautions  were  necessary.  Many  of  the 
darker  pupae,  shown  in  the  table  to  be  produced  by 
white  and  gilt  surroundings,  were  proved  to  have 
been  influenced  'by  mutual  proximity,  so  that  the 
results  would  have  been  even  more  striking  if  this 
source  of  error  had  been  allowed  for. 


124  THE  COLOUKS  OF  ANIMALS 


The  period  during  which  the  colours  of  pupae  are 
determined 

A  very  large  number  of  experiments  and  the 
closest  and  most  frequent  observations  were  devoted 
to  the  determination  of  the  time  during  which  these 
organisms  are  sensitive  to  surrounding  colours.  It 
was  first  necessary  to  observe  everything  that  happens 
to  a  caterpillar  between  the  cessation  of  feeding  and 
the  change  into  a  chrysalis,  for  I  felt  sure  that  the 
time  of  susceptibility  lay  somewhere  within  these 
limits.  When  one  of  these  caterpillars  is  full-fed, 
it  descends  from  its  food-plant  (nettle)  and  wanders 
about  in  search  of  some  suitable  surface  upon  which 
to  pass  the  pupal  period.  This  is  stage  i.,  and  its 
length  varies  greatly,  according  to  the  proximity  of 
suitable  surfaces.  Then  the  caterpillar,  having  found 
the  surface,  rests  motionless  upon  it,  generally  in  a 
somewhat  curved  position.  This  is  stage  ii.,  and  it 
is  also  variable  in  length,  but  fifteen  hours  may  be 
accepted  as  a  fair  average  of  the  time  spent  in  this 
position.  Finally  the  caterpillar  hangs,  head  down- 
wards, suspended  by  its  last  pair  of  claspers  (larval 
legs),  which  are  attached  to  a  boss  of  silk  spun  at  the 
close  of  the  second  stage.  This  is  stage  iii.,  which 
lasts  for  about  eighteen  hours,  at  the  end  of  which 
time  the  skin  splits  along  the  back  behind  the  head, 
and  the  chrysalis  is  exposed  by  the  skin  being  worked 


VAKIABLE  PROTECTIVE  EESEMBLANCE  IN  INSECTS      125 

up  towards  the  boss  of  silk.  Then  the  tail  of  the 
chrysalis  is  withdrawn  from  the  interior  of  the  skin 
and  is  forced  up  the  outside  of  the  latter,  until  it 
comes  in  contact  with  the  boss  of  silk.  Contact 
immediately  causes  some  of  the  numerous  hooks  on 
the  end  of  the  chrysalis  to  be  entangled  in  the  silk. 
During  this  apparently  perilous  operation  the  chrysa- 
lis is  suspended  to  the  larval  skin,  although  different 
opinions  obtain  as  to  the  exact  method  of  its  attach- 
ment. The  sight  is  extremely  interesting  and  beautiful, 
and  the  operation  is  almost  always  performed  with 
precision  and  success.  As  soon  as  the  pupa  is  firmly 
attached  to  the  silk,  it  endeavours,  by  the  most  violent 
movements,  to  get  rid  of  the  skin,  and  generally 
succeeds  in  detaching  it. 


Exact  determination  of  the  period  of  susceptibility 

The  whole  of  the  period  before  pupation,  including 
the  three  stages,  may  be  estimated  at  about  thirty-six 
hours.  Even  if  the  caterpillars  were  susceptible 
during  stage  i.,  no  effective  results  could  be  obtained ; 
for  they  are  then  wandering  over  surfaces  of  various 
colours,  of  which  few  can  be  the  same  as  that  which 
will  form  the  environment  of  the  chrysalis.  Many 
experiments  were  conducted  with  the  object  of  as- 
certaining the  exact  period  of  susceptibility.  Larvae 
were  exposed  to  one  colour  during  stages  i.  and  ii., 
and  then  transferred  to  another  colour  for  stage  iii., 
7 


126 


THE  COLOURS  OF  ANIMALS 


•while  other  larvse  were  exposed  to  each  of  the  colours 
for  all  three  stages  :  the  effects  were  then  compared. 
The  results  of  the  largest  experiment  of  the  kind  are 
given  below : — 


! 

Degrees  of  colour 

Dark 

Light 

,2 

(as  before)                       (1) 

W 

(3) 

(») 

(3) 

(*) 

(6) 

-5 

In  black  surroundings  for  all 

three  stages     .         .         .    — 

1 

— 

6 

— 

1 

— 

=    7 

Transferred  from  black  into 

gilt  for  stage  iii.       .         .    — 

— 

— 

1 

5 

3 

— 

=    9 

Transferred  from  gilt   into 

black  for  stage  iii.    .         .    — 

— 

— 

— 

6 

9 

— 

=  15 

In   gilt  surroundings  for  all 

three  stages     .         .        .    — 

— 

— 

5 

7 

8 

=  20 

I 

51 

This  analysis  speaks  for  itself.  Stages  ii.  and  iii.  are 
both  sensitive,  but  stage  iii.  is  much  less  sensitive 
than  the  other.  This  is  proved  by  the  fact  that  the 
larvae  which  had  been  exposed  to  gilt  surroundings 
during  stage  ii.  and  to  black  afterwards,  were  lighter 
thm  those  which  had  been  exposed  to  black  during 
stage  ii.  and  to  gilt  afterwards.  In  other  words,  the 
coloured  surroundings,  both  gilt  and  black,  produced 
more  effect  during  stage  ii.  than  iii. ;  but  both  stages 
are  sensitive,  because  the  black  and  gilt  surroundings 
produced  still  greater  effects  when  they  operated  for 
the  whole  period  before  pupation.  It  must  be  ob- 
served that  the  caterpillars,  in  the  experiment  sum- 
marised above,  tended  as  a  whole  to  produce  the 
lighter  forms  of  chrysalides,  so  that  the  black  did 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    127 

not  cause  nearly  such  strong  effects  as  the  gilt  sur- 
roundings. The  tendency  was  evidently  hereditary 
and  shared  by  all  the  caterpillars  of  the  company,  so 
that  we  have  a  striking  example  of  the  errors  which 
were  eliminated  by  keeping  the  companies  separate. 

It  is  almost  unnecessary  to  point  out  how  com- 
pletely the  old  theory  of  '  photographically  sensitive  ' 
chrysalides  is  broken  down  by  these  experiments. 
Not  only  is  the  adjustment  of  the  pupal  colours  to 
their  surroundings  due  to  larval  susceptibility,  but 
the  larva  itself  has  ceased  to  be  highly  sensitive  many 
hours  before  pupation  takes  place.  And  this  is  to  be 
expected,  for  during  the  latter  part  of  stage  iii.  rapid 
changes  are  going  on  beneath  its  surface,  and  the 
developing  pupa  is  becoming  loosened  from  the  larval 
skin  which  encloses  it  like  a  shell.  Putting  together 
the  results  of  all  the  experiments,  it  is  probable  that 
in  this  species  the  influence  of  surrounding  colours 
operates  upon  the  larva  during  the  twenty  hours 
immediately  preceding  the  last  twelve  hours  of  the 
larval  state.  Hence  stage  ii.  is  the  great  period  of 
susceptibility,  and  this  is  probably  the  true  meaning 
of  the  hours  during  which  the  caterpillar  rests  motion- 
less on  the  surface  upon  which  it  will  pupate ;  while 
stage  iii.  has  other  meanings  connected  with  the  rapid 
pupal  development  which  is  taking  place. 


128         THE  COLOURS  OF  ANIMALS 


Determination  of  the  part  affected  by  surrounding 
colours 

Having  thus  defined  the  time  of  susceptibility,  the 
next  question  was  to  ascertain  the  organ  or  part  of 
the  larva  which  is  sensitive.  At  first  it  appeared 
likely  that  the  larvae  might  be  influenced  through  their 
eyes  (ocelli),  of  which  they  have  six  on  each  side  of  the 
head.  Hence  in  many  experiments  the  eyes  of  some 
of  the  larvae  were  covered  with  an  innocuous  opaque 
black  varnish,  and  they,  together  with  an  equal  number 
of  normal  larvae  from  the  same  company,  were  placed 
in  gilt  or  white  surroundings.  The  pupae  from  both 
sets  of  larvae  were,  however,  always  equally  light- 
coloured.  It  then  seemed  possible,  although  highly 
improbable,  that  the  varnish  itself  might  act  as  a 
stimulus  similar  to  that  caused  by  white  or  gilt 
surroundings,  and  therefore  the  experiment  was  re- 
peated with  black  surroundings  in  darkness ;  but  the 
pupae  of  the  two  sets  were  again  almost  identical,  so 
that  it  appeared  certain  that  the  eyes  can  have 
nothing  to  do  with  the  influence. 

It  then  seemed  possible  that  the  large  branching 
bristles,  with  which  the  larvae  are  covered,  might  con- 
tain some  organ  which  was  affected  by  surround- 
ing colours,  but  experiments  in  which  half  of  the 
larvae  were  deprived  of  their  bristles  showed  con- 
clusively that  the  sensitive  organs  must  have  some 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   129 

other  position,  for  the  pupse  from  both  sets  of  larvae 
were  identical. 

I  was  thus  driven  to  the  conclusion  that  the 
general  surface  of  the  skin  of  the  caterpillar  is  sensi- 
tive to  colour  during  stage  ii.  and  part  of  stage  iii. 
In  order  to  test  this  conclusion  I  wished  to  subject 
the  body  of  the  same  larva  to  two  conflicting  colours, 
such  as  black  and  gold,  producing  the  most  opposite 
effects  upon  the  pupa.  Such  an  experiment,  if 
successfully  carried  out,  would  decide  some  important 
points.  If  the  part  of  the  body  containing  the  head 
was  not  more  sensitive  than  the  other  part,  a  valuable 
confirmation  of  the  blinding  experiments  would  be 
afforded.  Mrs.  Barber's  suggestion  that  parti- coloured 
pupae  may  be  produced  by  the  influence  of  two  colours 
would  be  tested  in  a  very  complete  manner ;  if  parti- 
coloured pupae  were  obtained  it  seemed  probable  that 
the  light  acts  directly  upon  the  skin,  but  if  they  could 
not  be  obtained  it  seemed  more  probable  that  the 
light  influences  the  termination  of  nerves  in  the  skin, 
and  that  the  pupal  colours  are  produced  through  the 
medium  of  the  nervous  system. 

The  practical  difficulties  in  the  way  of  such  an  ex- 
periment were  very  great,  for  the  conflicting  colours 
could  only  be  applied  during  stage  iii.,  when  the  larva 
is  motionless  and  may  be  disturbed  with  impunity. 
If,  on  the  other  hand,  a  larva  be  disturbed  in  stage 
ii.  it  begins  to  walk  about  and  thus  renders  the 
experiment  impossible.  The  only  way  to  obtain 


130         THE  COLOUES  OF  ANIMALS 

satisfactory  results  in  spite  of  the  slight  susceptibility 
of  stage  iii.  was  to  employ  large  numbers  of  larvaa, 
and  to  pay  careful  attention  to  minute  differences  of 
pupal  colour  as  well  as  to  the  time  during  which  the 
conflicting  colours  had  been  applied. 

The  experiments  were  conducted  in  two  ways. 
In  the  first  the  larvae  were  induced  to  suspend  them- 
selves from  sheets  of  clear  glass,  by  placing  them  in 
wide  shallow  glass  boxes  so  that  the  ascent  to  the 
glass  roof  was  easily  accomplished..  As  soon  as  sus- 
pension (stage  iii.)  had  taken  place,  each  larva  was 
covered  with  a  cardboard  tube  divided  into  two 
chambers  by  a  horizontal  partition  which  was  fixed 
rather  below  the  middle.  There  was  a  central  hole 
in  the  partition  just  large  enough  to  admit  the  body 
of  the  larva.  The  tube  was  fixed  to  the  glass  sheet 
with  glue;  the  upper  chamber  was  lined  with  one 
colour,  e.g.  gilt,  and  the  lower  chamber  with  the 
opposite  colour,  e.g.  black,  with  which  the  outside  of 
the  cylinder  was  also  covered,  in  case  the  larva  should 
stretch  its  head  beyond  the  lower  edge.  The  parti- 
tion was  fixed  at  such  a  height  that  the  larval  head 
and  rather  less  than  half  of  the  total  surface  of  skin 
were  contained  in  the  lower  chamber,  while  rather 
more  than  half  of  the  skin  surface  was  contained  in 
the  upper  chamber.  The  arrangement  is  shown  in 
section  in  fig.  30. 

The  second  method  of  conducting  the  conflicting 
colour  experiments  was  superior  in  the  more  equal  illu- 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    131 


mination  of  the  upper  and  lower  colours.  The  bottom 
of  a  shallow  wooden  box  was  covered  with  alternate 
areas  of  black  and  gilt  paper,  and  partitions  were 
fixed  along  the  lines  where  the  two  colours  came  into 
contact.  Each  par- 
tition was  gilt  to- 
wards the  gilt  surface 
and  black  towards 
the  black,  and  was  c 
perforated  close  to 
the  bottom  of  the 
box  with  holes  which 
would  just  admit  the 
body  of  a  larva.  The 
box  was  then  placed 
in  a  vertical  position 
towards  a  strong 
light,  so  that  the 
partitions  became 

horizontal  shelves,  while  the  black  and  the  gilt  sur- 
faces were  uppermost  alternately.  As  soon  as  a  larva 
was  suspended  to  a  glass  sheet,  the  boss  of  silk  was 
carefully  scraped  off  and  was  pinned  on  the  upper  colour 
above  one  of  the  holes,  so  that  the  head  and  first  five 
body-rings  passed  through  the  hole  on  to  the  colour 
beneath,  which  tended  to  produce  opposite  effects. 
Other  larvae  were  similarly  fixed  between  the  shelves 
upon  one  colour  only,  so  as  to  afford  a  comparison 
with  the  results  of  the  conflicting  colours. 


FIG.  30.— The  larva  of  Small  Tortoiseshell  Butter- 
fly suspended  in  a  tube  of  which  the  upper 
compartment  is  lined  with  gilt,  the  lower  with 
black ;  x  2.  s.  Boss  of  silk.  b.  Black,  c.  Card- 
board, g.  Gilt. 


132         THE  COLOURS  OF  ANIMALS 

A  careful  comparison  of  all  the  pupse  obtained  in 
the  conflicting  colour  experiments  showed  that,  when 
the  illumination  of  the  two  surfaces  was  equal,  the 
effective  results  were  produced  by  that  colour  to 
which  the  larger  area  of  skin  had  been  exposed, 
whether  the  head  formed  part  of  that  area  or  not. 
Parti-coloured  pupae  were  never  obtained.  It  there- 
fore appears  to  be  certain  that  the  skin  of  the  larva 
is  influenced  by  surrounding  colours  during  the  sensi- 
tive period,  and  it  is  also  probable  that  the  effects  are 
wrought  through  the  medium  of  the  nervous  system. 
This  latter  conclusion  receives  further  confirmation 
from  other  observations  which  will  be  described  in  the 
next  chapter  (see  pp.  142-  ^1G). 


CHAPTER  IX 

VARIABLE  PROTECTIVE  RESEMBLANCE  IN 
INSECTS   (continued) 

The  meaning  of  the  metallic  appearance  of  pupae 

APART  from  the  general  physiological  significance  of 
the  results  described  in  the  last  chapter,  they  are  of 
extreme  interest  in  giving  us  a  possible  clue  to  the 
meaning  of  the  remarkable  metallic  appearance  of 
the  pupae  of  many  butterflies.  This  wonderful  appear- 
ance has  given  the  name  chrysalis  to  the  second 
stage  of  Lepidopterous  metamorphosis,  although  rela- 
tively few  pupae  are  really  entitled  to  bear  it.  But 
some  pupae  which  deserve  the  name  are  very  common, 
and  probably  have  attracted  attention  ever  since  men 
began  to  look  with  interest  on  the  world  around  them. 
Not  only  did  the  alchemists  believe  that  in  the  appear- 
ance of  these  animals  they  received  encouragement 
for  the  successful  issue  of  the  projects  which  were 
always  before  them,  but  we  find  that  Aristotle,  writing 
more  than  2,200  years  ago,  mentions  chrysalis  as  a 
word  which  was  generally  used  *  in  his  time,  and  which 
had  therefore  been  invented  as  descriptive  of  the 


134  THE  COLOURS  OF  ANIMALS 

golden  appearance  at  a  still  earlier  period.  There  can 
be  no  doubt  of  this,  for  Aristotle's  word  is  xpva-a\\is, 
identical  with  our  own ;  nor  can  there  be  any  doubt 
as  to  the  stage  of  insect  life  to  which  Aristotle  was  refer- 
ring, for  his  language  is  precise  and  descriptive.  In 
fact,  if  a  naturalist  wished  to  convey  to  any  one  igno- 
rant of  the  changes  undergone  in  insect  metamorphosis 
a  short  and  simple  but  perfectly  accurate  account  of 
the  two  first  stages  of  a  Lepidopterous  insect,  he  could 
not  do  better  than  use  the  very  words  of  Aristotle : 
'  Caterpillars  take  food  at  first,  but  afterwards  they 
cease  to  take  it  and  become  quiescent,  being  generally 
called  chrysalides ;  ' !  or  again  in  another  passage  : 
'Afterwards  the  caterpillars,  having  grown,  become 
quiescent,  change  their  shape,  and  are  called  chrysa- 
lides.' 3 

Mr.  T.  W.  Wood  suggested  that  the  metallic 
appearance  was  so  essentially  unlike  anything  usually 
found  in  the  organic  kingdoms,  that  it  acted  as  a 
protection  to  the  organisms  possessing  it.  Others 
have  thought  that  it  has  the  value  of  a  warning 
colour,  indicating  an  unpleasant  taste  (see  Chapter 
X.).  It  is  probable  that  the  appearance  sometimes 
bears  this  meaning  now,  but  it  is  unlikely  that  such 
was  its  original  use ;  for  the  fact  that  metallic  colours 
can  be  called  up  or  dismissed  by  the  appropriate  sur- 

1  o?  re  yap  Ka.fj.vai  \afi.&avovffi  rii  vpurov  Tptxpfyv,  yueri  ravra  ovKtrt 

i',  d\A.'  aKivtiTi^ovfflv  al  KaAov/j.ei/ai  \nr&  Tivtav  xpWAAfSes. 
iiero  5£  -ravra  (at    Ka.fj.ifui]    av|7j0«i<rat    a.Kwriri^oL.(ri>   ical 
T^V  (iop<t>1)v,  ical  KaXovvrai 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    135 

roundings  shows  that  they  are  essentially  protective, 
and  as  far  removed  as  possible  from  conspicuous 
warning  colours,  the  object  of  which  is  to  render  their 
possessors  unlike  the  environment.  What  can  be  the 
object  in  nature  which  the  glittering  pupae  resemble  ? 
It  is  obvious  that  metals  are  not  sufficiently  abun- 
dant on  the  surface  of  the  earth  to  afford  models  for 
successful  imitation,  and  there  is  the  same  objection 
to  certain  metallic  sulphides  which  otherwise  would 
answer  the  purpose  admirably. 

A  consideration  of  the  darker  non-glittering  va- 
rieties of  the  same  species  helps  us  to  an  explana- 
tion. These  certainly  resemble  the  grey  surface  of 
weathered  rocks,  and  the  whole  shape  of  such  pupae, 
with  their  angular  projections  and  tubercles,  com- 
bines with  their  colour  to  produce  a  most  perfect 
Protective  Kesemblance  to  rough  dark  surfaces  of 
rock.  In  fact,  did  we  not  delude  the  larvae  by  offering 
them  flat  mineral  surfaces  in  our  walls  and  sides  of 
houses,  the  protection  would  be  so  complete  that 
we  should  hardly  ever  find  the  chrysalides ;  and,  as 
a  matter  of  fact,  they  are  rarely  seen  except  in  such 
situations. 

In  England  we  very  rarely  see  a  brightly  metallic 
pupa  because  in  our  moist  climate  exposed  rock- 
surfaces  quickly  weather  and  become  lichen-covered. 
If,  however,  the  bright  appearance  of  many  recently 
fractured  rocks  were  retained,  as  they  are  in  drier 
countries,  they  would  cause  the  production  of  a  similar 


136  THE  COLOUES  OF  ANIMALS 

appearance  in  the  pupae  of  those  larvae  which  sought 
them. 

Although  metallic  surfaces  are  not  conspicuous  in 
nature,  there  is  a  very  abundant  glittering  mineral 
•which  is  quite  common  enough  to  offer  a  surface 
against  which  the  larvae  might  often  suspend  them- 
selves. I  refer  to  the  mineral  mica,  the  substance 
forming  the  glittering  flakes  which  are  so  well-known 
in  common  granite.  Furthermore,  any  recently 
broken  rock  contains  bright  and  glittering  surfaces, 
although  they  may  not  be  so  brilliant  as  mica,  and 
the  bright  spots  of  the  pupae  would  thus  be  of  pro- 
tective value  against  almost  any  freshly  exposed 
mineral  surface. 

Hence  we  see  that  the  pupae  would  occur  as  dark 
or  glittering  forms,  as  the  surrounding  mineral  sur- 
faces are  dark  or  glittering :  they  appear  in  two 
different  varieties  which  are  respectively  in  harmony 
with  the  two  conditions  of  the  mineral  surfaces  they 
resemble — the  dark  and  weathered,  and  the  bright 
and  freshly  exposed  condition. 

It  may  be  that  this  adaptation  to  mineral  sur- 
roundings arose  when  the  widespread  green  tints  of 
the  vegetable  kingdom  contributed  less  to  the  total 
appearance  of  land-surfaces ;  or  the  adaptation  may 
have  followed  the  habit  of  feeding  upon  herbaceous 
plants  which  withered  away  in  the  hot  season, 
changing  from  green  to  brown  during  the  time  when 
the  insect  was  in  the  chrysalis  state  and  could 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   137 

undergo  no  corresponding  change  of  colour.  How- 
ever the  adaptation  arose  in  the  ancestor  of  all  butter- 
flies which  now  emerge-  from  gilded  chrysalides,  it  is 
probable  that  it  took  place  in  some  hot  dry  country, 
where  mineral  surfaces  did  not  weather  quickly  but 
remained  glittering  for  long  periods  of  time. 


The  manner  in  which  golden  chrysalides  are  adapted 
for  concealment  on  plants 

In  the  origin  and  gradual  progress  of  our  modern 
aggressive  forms  of  vegetation,  less  and  less  of  the 
land-surface  has  been  formed  by  mineral  substances, 
until  the  green  colour  of  foliage  and  the  brown  colour 
of  stems  and  of  withered  leaves  have  become  the  pre- 
dominant tints  of  nature  and  the  most  feasible  models 
for  Protective  Eesemblance.  It  is  therefore  interesting 
to  note  how  the  species  with  gilded  pupse  have  adapted 
themselves  to  the  change. 

The  chrysalis  of  the  Peacock  Butterfly  (Vanessa  lo) 
still  retains  the  dark  variety,  which  is  formed  when 
pupation  takes  place  upon  dark  rock  surfaces  ;  but  the 
golden  form  has  been  replaced  by  a  green  variety, 
which  is  produced  when  the  chrysalis  is  suspended 
from  the  leaves  of  its  food-plant.  The  green  variety 
still  retains  the  metallic  appearance,  and  exhibits  it 
to  a  much  greater  extent  than  the  dark  variety. 
During  the  summer  of  1888  I  found  that  the  green 
form  is  produced  by  the  surroundings  which  cause 


138         THE  COLOURS  OF  ANIMALS 

the  appearance  of  the  gilded  form  of  the  Small 
Tortoiseshell  chrysalis,  viz.  by  a  gilt  and  by  a  white 
environment. 

The  chrysalis  of  the  Eed  Admiral  Butterfly 
(Vanessa  Atalanta)  has  no  green  variety,  but  it  appears, 
like  the  Small  Tortoiseshell,  as  a  dark  or  a  glittering 
form  resembling  the  two  conditions  of  rock-surfaces 
upon  which  it  often  pupates,  hanging  suspended 
without  any  attempt  at  concealment  except  such  as  is 
afforded  by  its  very  perfect  colour-harmony  with  the 
surroundings.  I  have  shown  that  this  species  also  is 
susceptible,  and  that  either  variety  of  pupa  is  produced 
by  the  appropriate  environment.  But  this  chrysalis 
is  very  commonly  found  attached  to  the  food-plant, 
and  when  this  is  the  case  it  hangs  suspended  in  a 
tent  formed  of  leaves  carefully  spun  together  by  the 
caterpillar,  so  that  it  is  concealed  from  view.  The 
larva  also  often  has  the  habit  of  partially  biting 
through  the  leaf-stalk  or  stem,  so  that  the  leaves  of 
its  retreat  hang  down  and  wither.  The  dead  brown 
leaver  thus  afford  a  far  more  harmonious  background 
for  the  dark  pupa,  if  by  any  chance  it  becomes 
exposed  to  view. 

The  Small  Tortoiseshell  has  neither  the  green 
variety  of  the  Peacock  nor  the  protective  habit  of 
the  Eed  Admiral,  and  therefore  it  almost  invariably 
seeks  mineral  surroundings  for  the  pupal  period,  and 
very  rarely  becomes  a  chrysalis  on  its  food-plant. 
In  1886  I  only  found  three  such  pupse  suspended  to 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   139 

the  food-plant,  although  I  examined  the  nettle-beds 
where  many  hundreds  of  caterpillars  had  been  feeding 
and  had  left  for  pupation.  All  these  three  pupae  were 
dead,  being  filled  with  the  parasitic  larvae  of  Ichneumon 
flies.  In  1888  I  found  many  more  pupae  upon  the 
food-plant,  but  a  very  high  percentage  of  these  had 
been  killed  by  parasites,  and  the  hurrying  on  of 
pupation  which  occurred  in  the  other  cases  and  pre- 
vented the  larvae  from  wandering  in  a  normal  manner 
may,  I  think,  be  attributed  to  the  state  of  health 
induced  by  that  extraordinarily  wet  season. 


The  colours  of  certain  dimorphic  pupae  cannot  be  adjusted 
to  the  surroundings 

I  have  already  mentioned  that  I  experimented 
upon  the  pupae  of  the  Swallow-tailed  Butterfly 
(Papilio  machaori),  and  found  that  they  were  not  sus- 
ceptible to  the  influence  of  surrounding  colours.  This 
is  also  true  of  the  small  family  of  Mocha  moths 
(Ephyrida)  which  have  freely  exposed  pupae,  fixed 
like  those  of  many  butterflies  by  a  silken  girdle  and 
boss,  and  often  appearing  in  two  varieties,  green  and 
brown.  The  caterpillars  of  the  same  species  are  also 
of  two  colours,  and  always  produce  pupae  of  corre- 
sponding tints  (see  page  46). 


140         THE  COLOURS  OF  ANIMALS 


Variable  Protective  Resemblance  in  the  pupae  of  the 
Pieridae. 

The  susceptibility  of  the  two  species  of  Garden 
White  Butterflies  (Pieris  brassica  and  P.  rapes)  was 
also  investigated  in  the  same  season  (1886),  and  the 
results  of  previous  observers  were  confirmed  and 
extended.  Many  colours  were  employed,  and  it  was 
found  that  the  light  reflected  from  yellow  and  orange 
surroundings  was  very  potent  in  producing  bright 
green  varieties  of  the  chrysalides  of  both  species.  It 
is  therefore  probable  that  when  the  light  reflected 
from  green  leaves  produces  this  effect  in  nature,  the 
yellow  and  orange  constituents  of  the  light  form 
the  stimuli.  When,  therefore,  these  constituents  are 
made  use  of  nearly  alone,  they  produce  still  more 
marked  effects.  Black  and  white  backgrounds  caused 
the  pupae  of  both  species  to  become  dark  and  light 
respectively,  and  all  other  colours  except  yellow  and 
orange  produced  more  or  less  dark  pupae. 

Experiments  were  made  upon  P.  rapce,  to  ascertain 
the  susceptible  period,  the  larvae  being  transferred  as 
in  the  case  of  the  Small  Tortoiseshell.  The  results 
were  as  in  the  latter :  the  larva  is  sensitive  and  not 
the  pupa,  and  the  time  of  chief  susceptibility  is  during 
stage  ii. 

A  few  larvae  of  P.  rapce  were  blinded,  but  the  chry- 
salides were  similar  to  those  produced  by  normal  larvae. 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   141 


Further  experiments  on  the  same  subject 

During  the  summer  of  1888  I  conducted  further 
experiments  upon  the  same  subject.  The  results  are 
as  yet  imperfectly  worked  out,  and  are  unpublished, 
but  I  will  shortly  mention  the  chief  conclusions. 
Other  glittering  metallic  surfaces,  such  as  silver  or  tin, 
do  not  produce  anything  like  so  striking  an  effect  as 
gold  upon  the  pupaB  of  the  Small  Tortoiseshell.  It 
seems  probable  that  the  yellow  light  reflected  from 
the  gold  is  effective  in  preventing  the  formation  of 
pigment,  and  in  thus  producing  the  gilded  chrysalides, 
just  as  the  yellow  light  also  prevents  the  appearance 
of  pigment  and  produces  the  bright  green  pupae  among 
the  Pierida. 

Two  new  species  also  were  investigated,  and  proved 
to  be  sensitive.  The  pupae  of  the  Silver-washed 
Fritillary  (Argynnis  paphia)  can  be  rendered  dark  or 
light  in  colour,  although  the  metallic  spots  do  not 
seem  to  be  affected.  The  pupae  of  the  Large  Tortoise- 
shell  (Vanessa  polycTiloros)  were  also  rendered  dark 
brown  without  metallic  spots,  or  light  reddish-brown 
with  the  spots,  by  the  use  of  appropriate  surroundings. 
The  metallic  spots  could  not  be  extended  over  the 
pupal  surface  as  in  the  case  of  the  Small  Tortoise- 
shell. 


142          THE  COLOUKS  OF  ANIMALS 


Confirmatory  results  obtained  by  other  workers 

It  is  also  interesting  to  record  that  many  of  these 
results  have  been  since  confirmed  by  independent 
workers.  Mr.  G.  C.  Griffiths  worked  at  the  chrysalis 
of  the  Small  Garden  White  (Pieris  rapce),  and  con- 
firmed my  results  in  many  important  respects.1  The 
Eev.  J.  W.  B.  Bell  and  Mr.  Pembrey  have  worked  at 
the  pupae  of  the  Small  Tortoiseshell  and  Peacock,  and 
the  former  also  at  the  pupse  of  the  Large  Tortoise- 
shell.2  Their  results  are,  on  the  whole,  confirmatory 
of  those  described  above. 


Variable  Protective  Resemblance  in  the  colours 
of  cocoons 

It  has  been  already  mentioned  that  the  colour  of 
the  cocoon  in  certain  species  can  be  adjusted  to  the 
environment.  I  obtained  proof  of  this  in  1886,  at 
the  suggestion  of  Mr.  W.  H.  Harwood  of  Colchester, 
who  had  observed  that  the  colour  of  the  cocoon  of  the 
Emperor  Moth  (Saturnia  carpini)  varied,  and  seemed 
to  suit  its  environment.  I  found  that  caterpillars  of 
this  species  spun  very  dark  brown  cocoons  in  a  black 
calico  bag  (see  fig.  31),  while  white  cocoons  were 


Trans.  Ent.  Soc.  Lond.  1888,  pp.  247  et  seq. 
The  Midland  Naturalist,  Dec.  1889,  pp.  289-90. 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   143 

spun   in  white   surroundings  in  a  strong  light  (see 
fig.  82). » 

In  this  case  it  seems  almost  impossible  for  the 
surrounding  colours  to  influence  directly  the  colour  of 
the  cocoon.  It  is  necessary  to  assume  the  existence 


FIG.  31.— The  cocoon  of  Emperor  Moth  PIG.  32.— The  cocoon  of  Emperor  Moth, 

(S.  carpini),  spun  in  a  black  calico  spun  on  a  white  surface  in  strong 

bag  ;  natural  size,  although  an  excep-  light ;  natural  size, 
tionally  small  cocoon. 

of  a  complex  nervous  circle  as  a  medium  through 
which  the  stimulus  of  colour  can  make  itself  felt.  If 
this  conclusion  be  correct  it  is  probable  that  the 
colours  of  the  pupa  and  larva  are  adjusted  in  the 
same  manner. 

The  observation  upon  S.   carpini  has   been  con- 

1  Proc.  Hoy.  Soc.  vol.  xlii.  p.  108.  I  have  since  found  that  the 
fact  must  have  been  known  previously,  for  it  is  quoted  in  Mr.  A.  R. 
Wallace's  Tropical  Nature.  I  do  not  yet  know  the  name  of  the 
naturalist  who  made  the  observation. 


144         THE  COLOURS  OF  ANIMALS 

firmed,  and  has  been  extended  to  other  species.  Thus 
Kev.  W.  J.  H.  Newman  showed  that  the  cocoons  of  the 
Small  Eggar  Moth  (Eriogaster  lanestris)  are  creamy 
white  when  spun  upon  white  paper  (see  fig.  33) ,  dark 


FIG.  33. — The  cocoon  of  Small  Eggar       PIG.  34. — The  cocoon  of  Small  Eggar 
Moth  (E.  lanestris),  spun  upon  white  spun  among  green  leaves, 

paper ;  natural  size. 

brown  when  constructed  among  leaves  (see  fig.  34) -1 
These  cocoons  are  so  compact  and  smooth  that  they  re- 
semble birds'  eggs  :  a  fact  which  explains  the  name  of 
the  moth.  In  constructing  the  cocoon  the  caterpillar 
leaves  a  few  holes,  which  are  doubtless  of  importance 
in  permitting  a  free  exchange  of  air.  The  fact  that 
light  reflected  from  green  leaves  is  here  the  stimulus 
for  the  production  of  a  dark  colour  is  readily  intelligible 
when  we  remember  that  the  moth  does  not  emerge  till 
the  following  February  at  the  earliest,  while  the  in- 
sect often  remains  in  the  pupal  state  for  one  or  two 
years  longer.  The  leaves  in  contact  with  the  cocoon 
soon  die  and  turn  brown,  and  after  this  change  the 
dark  colour  is  highly  protective.  It  is  also  of  especial 
importance  for  the  cocoon  to  be  well  concealed  during 
the  winter  months,  when  insect-eating  animals  are 

1  /Yoc.  Ent.  Soc.  Land.  1887,  pp.  1.  li. 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    145 

pressed  for  food,  and  are  obliged  to  search  for  it  with 
extreme  care. 

I  have  also  shown  that  the  cocoon  of  the  Green 
Silver  Lines  Moth  (Halias  prasinand)  can  be  modified  in 
colour  like  that  of  the  Small  Eggar.1  This  species  also 
passes  the  winter  in  the  chrysalis  state,  when  the  brown 
colour  is  highly  protective.  One  of  my  caterpillars 
had  begun  to  spin  a  brown  cocoon  upon  an  oak  leaf 
(see  fig.  35).  I  then  removed  the  caterpillar  to  a  white 
box  ;  it  remained  motionless  for  several  hours  and  then 


FIG.  36. — White  cocoon  spun  by  same 
caterpillar  when  transferred  from 
oak  leaf  to  white  paper;  natural 


Fio.  35. — Brown  oocoon  begun 
by  caterpillar  of  Green  Silver 
lines  Moth  (fi.prasinana)\ifOQ 
an  oak  leaf ;  natural  size. 


FIG.  37, — The  brown  oocoon  of 
Green  Silver  Lines  spun  upon 
an  oak  leaf. 


spun  a  white  cocoon  (see  fig.  36).  The  brown  cocoon 
of  the  same  species  is  shown  in  fig.  37.  Remembering 
the  experiments  upon  the  Small  Tortoiseshell,  it  is 
very  probable  that  the  colour  of  the  cocoon  was  deter- 


Proc.  Ent.  Soc.  Lond.  1887,  pp.  1.  li. 


146         THE  COLOUES  OF  ANIMALS 

mined  during  the  time  when  the  caterpillar  was 
motionless  in  the  box. 

Still  later  in  1888  Dr.  E.  G.  Lynam  sent  me  some 
cocoons  of  the  Gold-tail  Moth  (Liparis  auriflua)  which 
had  been  also  modified  in  a  similar  manner,  and  I 
found  that  the  same  power  is  possessed  by  the  cater- 
pillar of  the  Brimstone  Moth  (Rumia  crat&gatd)  .l  In 
this  latter  case  a  green  tissue-paper  background  pro- 
duced brown  cocoons  like  those  spun  upon  green  leaves. 

It  is  probable  that  this  power  of  adjusting  the 
colour  of  the  cocoon  is  very  common  among  species 
which  spin  in  exposed  situations.  It  may  also  be 
expected  to  occur  in  those  Hymenoptera  with  similar 
habits.  The  investigation  of  the  physiological  pro- 
cesses involved  in  the  adjustment  would  be  of  extreme 
interest.  Last  year  (1888)  I  obtained  a  large  number 
of  Small  Eggar  caterpillars,  intending  to  begin  such 
an  investigation,  but  nearly  all  of  them  died  just 
before  reaching  maturity.  It  is  to  be  hoped  that 
many  species  will  now  be  tested  in  order  to  ascertain 
whether  this  form  of  susceptibility  is  present. 

Variable  Protective  Resemblance  in  Lepidopterous 
larvae 

It  now  remains  to  briefly  consider  the  power  of 
colour-adjustment   possessed   by  certain   caterpillars. 
Naturalists  have  long  known  that  in  certain  species 
1  Proc.  Ent.  Soc.  Land.  1888,  p.  xxviii. 


VARIABLE  PEOTECTIVE  KESEMBLANCE  IN  INSECTS   147 

the  colour  of  the  caterpillars  may  vary  according  to 
the  colour  of  the  plant  upon  which  they  are  found. 
This  is  especially  true  of  caterpillars  feeding  upon 
brightly  coloured  parts  of  the  plant,  such  as  the 
anthers  or  petals.  At  the  same  time  there  has  been, 
until  recent  years,  hardly  any  systematic  investigation 
of  these  interesting  facts.  Professor  E.  Meldola's 
editorial  notes  to  his  translation  of  Dr.  Weismann's 
'  Studies  in  the  Theory  of  Descent '  (the  essay  on 
'  The  Origin  of  the  Markings  of  Caterpillars  ')  contain 
many  instances  of  this  kind,  together  with  most  sug- 
gestive remarks  upon  them,  which  first  induced  me  to 
work  at  the  subject.  At  a  still  earlier  date  the  same 
writer  had  brought  together  all  the  scattered  examples 
of  this  kind,  including  the  power  of  adjusting  the 
colours  of  pupae,  and  had  drawn  attention  to  the 
general  principles  involved.1 


Experiments  upon  the  larva  of  the  Eyed  Hawk  Moth 

(Smerinthus  ocellatus) 

The  instance  which  Professor  Meldola  chiefly  con- 
siders in  his  editorial  notes  is  that  of  the  caterpillar 
of  the  Eyed  Hawk  Moth  (Smerinthus  ocellatus),  which 
is  of  a  whitish-green  colour  when  it  is  found  upon 
apple  and  certain  kinds  of  willow,  and  of  a  bright 
yellowish-green  when  found  upon  other  species  or 
varieties  of  willow. '  The  colours  are  on  the  whole 

1  Proc.  Zool.  Soc.  1873,  p.  153. 


148  THE  COLOURS  OF  ANIMALS 

protective;  the  larva  resembles  the  under  side  of  a 
rolled- up  leaf,  and  when  the  food-plant  bears  leaves 
with  white  and  downy  under  sides  (apple,  Salix 
viminalu,  &c.)  the  larva  is  usually  whitish ;  while  it 
is  generally  yellowish-green  upon  trees  of  which  the 
leaves  have  green  under  sides  (Salix  triandra,  S.  baby- 
lonica,  S.  rubra,  S.fragilis,  &c.).  I  remember,  when 
a  boy,  finding  the  two  varieties  of  larva,  and  being 
much  astonished  at  the  difference  between  them. 

I  began  working  at  the  species  in  1884,  and  have 
bred  large  numbers  of  the  larvae  for  every  season  since 
that  year.  Only  the  results  of  the  earlier  experiments 
are  published.1  The  eggs  of  each  female  moth  were 
kept  separate,  and  the  caterpillars  of  each  batch  were 
fed  upon  a  variety  of  food-plants,  and  manifested  de- 
cided differences  in  their  shade  of  green.  At  the  same 
time  remarkable  exceptions  occasionally  occurred : 
sometimes,  also,  when  collecting  I  have  found  bright 
green  individuals  upon  apple.  Blinding  experiments 
like  those  upon  the  Small  Tortoiseshell  led  to  negative 
results.  These  experiments  were  very  laborious,  for 
a  caterpillar  changes  its  skin  four  times,  and  with  it 
the  covering  to  its  eyes  and  the  opaque  varnish.  Hence, 
before  each  change  of  skin  the  caterpillars  were  sepa- 
rated from  the  food,  and,  after  changing  it,  were  re- 
blinded  before  being  restored. 

Before  this  investigation  had  been  begun,  it  waa 
believed  that  such  variability  in  caterpillars  was  due  to 

1  Proc.  Boy.  Soc.  vol.  xxxviii.  p.  269  ;  vol.  xl.  p.  135. 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS   149 

the  direct  chemical  effect  of  different  kinds  of  leaves 
upon  them  after  being  eaten,  and  it  was  therefore 
called  phytophagic  variability.  Many  special  experi- 
ments were  directed  toward  the  solution  of  this 
question.  Thus,  leaves  were  sewn  together,  so  that 
the  caterpillars  were  exposed  to  the  colour  of  the 
upper  or  of  the  under  side  alone,  although  they  ate 
the  same  leaf  in  both  cases.  In  other  instances  the 
'  bloom '  was  rubbed  off  the  under  sides  of  some  leaves 
(Salix  fragilis,  incorrectly  described  as  Triandra  in 
my  papers) ,  while  others  were  left  normal.  The  results 
proved  that  the  caterpillars  are  affected  by  the  colour 
of  the  leaves  and  not  by  the  leaves  as  food.  Com- 
parison with  the  experiments  on  pupae  renders  it 
most  probable  that  reflected  light  influences  the  skin. 


Experiments  upon  the  larvae  of  other  Sphingidse 

Professor  Meldola  had  also  quoted  the  instance  of 
the  larva  of  the  Privet  Hawk  Moth  (Sphinx  ligustri), 
which  is  of  a  much  brighter  green  when  found  upon 
privet  than  when  found  upon  lilac.  Larvae  of  this 
species,  from  the  same  batch  of  eggs,  were  fed  upon 
the  two  plants,  and  the  above  quoted  observation 
was  confirmed.  The  larvae  of  the  Lime  Hawk  Moth 
(Smerinthus  tilice)  were  similarly  modified,  being  made 
unusually  light  green  by  the  use  of  variegated  elm 
and  a  lime  having  leaves  with  very  white  and  downy 
under  sides. 

8 


ISO          THE  COLOUKS  OF  ANIMALS 


Experiments  upon  the  larvae  of  Geometrae  and  Noctuae 

The  experiments  were  then  extended  to  many 
other  dark-coloured  larvae  (chiefly  Geometree).  The 
method  of  experiment  was  as  follows  :  a  larva  which 
resembles  the  twigs  or  bark  of  its  food-plant  was 
selected,  and  was  surrounded  by  the  leaves  upon  which 
it  fed,  and  by  white  or  green  surfaces.  No  brown 
twig  or  anything  dark-coloured  was  allowed  to  come 
near  it  during  its  whole  life.  Under  these  circum- 
stances the  larvae,  in  the  majority  of  the  species  selected 
for  experiment,  became  very  light  brown  or  light  grey 
in  colour,  and  quite  unlike  the  darker  larvae  of  the 
same  kinds  which  were  produced  when  an  abundance 
of  dark  twigs  had  been  mixed  with  the  leaves  of  the 
food-plant.1 

The  results  were  certainly  protective,  for  the 
lighter  larvas  were  far  less  conspicuous  en  the  green 
leaves  and  stems  than  the  darker  ones  would  have 
been.  At  the  same  time  it  must  be  admitted  that  the 
resemblance  of  the  darker  forms  to  the  dark  branches 

1  These  experiments  have  been  successfully  applied  to  the  follow- 
ing Gcometrce : — Crocallis  elinguaria  (for  two  seasons),  Ennomos 
angularia,  E.  htnaria,  Boarmia  rhomboidaria  (this  species  was  inves- 
tigated by  my  friend  and  pupil,  Mr.  E.  C.  L.  Perkins,  B.A.,  of  Jesus 
College,  Oxford),  B.  roboraria ;  and  to  one  of  the  Noctuce,  Catocala 
sponsa,  Since  this  note  was  written,  I  have  found,  during  the  past 
summer  (1889),  that  the  Geometer  Heterophylla  abruptaria,  and  the 
Noctuas  Catocala  electa  and  C.  elocata,  are  also  sensitive,  the  first  and 
last  named  to  a  marked  degree. 


VAEIABLE  PKOTECTIVE  RESEMBLANCE  IN  INSECTS    151 

is  much  stronger  than  that  of  the  light  varieties  to 
the  leaves  (see  figs.  38  and  39).  Two  species,  how- 
ever, are  already  known  in  which  the  green  stems  and 


FIG  38.  The  larva  of  a  continental  Noctua  (Calocala  elocata)  with  the  colour 
adjusted  to  that  of  the  dark  twigs  mixed  with  its  food-plant ;  nearly  full-fed ; 
two-thirds  natural  size. 


FIG.  39. — The  colour  of  a  larva  of  the  same  species  when  only  preen  twigs  and  leaves 
were  supplied  to  it.  The  food-plant  in  both  cases  was  black  poplar  (Populut 
nigra). 

leaves  cause  the  production  of  green  larvae,  so  that  the 
concealment  is  very  perfect.  And  we  may  be  quite 
sure  tha,t  there  are  many  other  species  with  equal 
powers. 


Experiments  upon  the  larvae  of  the  Brimstone  Moth 

Lord  Walsingham  first  pointed  out  to  me  that  the 
larvse  of  the  Brimstone  Moth  (Eumia  cratcegata)  vary 
from  brown  to  green,  and  through  all  intermediate 
shades.  I  found  that  when  brown  objects  were 


152 


THE  COLOUKS  OF  ANIMALS 


entirely  excluded  the  larvae  became  greenish-brown, 
brownish-green,  or  sometimes  of  a  decided  green 
colour,  and  thus  harmonised  well  with  the  leaves  and 
young  green  twigs  of  the  hawthorn.  In  the  presence 
of  dark  twigs  they  became  dark  brown  like  so  many 
other  larvae.1 


Experiments  upon  the  larvae  of  the  Peppered  Moth 

The  second  instance  is  even  more  remarkable,  and 
has  only  been  observed  during  the  present  year  (1889). 
i  I    obtained    some 

hundreds  of  eggs 
from  a  single  wild 
female  of  the  Pep- 
pered Moth  (Am- 
phidasis  betularid), 
and  the  caterpillars 
which  hatched  were 
treated  as  in  the 
other  experiments. 
The  larvae  reared 
among  green  leaves 
and  shoots  became 

FIG.  41.— The  larva  of  Peppered  Moth  surrounded  by     bright     green     (866 
abundant  dark  twigs  as  well  as  leaves. 

fig.  40)  iciihout  ex- 
ception, while  the  others  in  nearly  all  cases  assumed 
the  colour  of  the  dark-brown  twigs,  which  were  mixed 

1  Report  of  the  British  Association,  1887,  p.  756 ;  also  Nature, 
vol.  36,  p.  594. 


FIG.  40.-The  larva  of  Peppered  Moth  (A.  betularia) 
surrounded  by  green  twigs  and  leaves  ;  full-fed  ; 
half  natural  size. 


VAKIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    153 

with  the  leaves  upon  which  they  fed  (see  fig.  41) : 
about  one  or  two  per  cent.,  however,  took  their  colour 
from  the  latter.  The  food-plants  were  the  same  in 
both  experiments. 


The  change  of  colour  is  not  due  to  the  food  seen  through 
a  transparent  skin 

Some  authorities  have  supposed  that  the  change 
of  colour  under  such  circumstances  is  a  comparatively 
simple  thing,  that  the  younger  green  leaves  eaten 
and  seen  in  the  alimentary  canal  through  the  more  or 
less  transparent  tissues  cause  a  brighter  appearance, 
while  the  older  leaves  produce  in  the  same  manner  a 
darker  appearance.  This  cause  of  colour  is  certainly 
efficient  in  many  transparent  caterpillars  (see  p.  79), 
such  as  some  of  the  Noctua,  but  it  does  not  account 
for  any  of  the  results  obtained  in  my  experiments. 

As  a  precaution  against  such  an  error,  I  reversed 
the  surroundings  of  a  few  larvae  of  most  of  the  species 
experimented  upon.  The  new  conditions  were  main- 
tained for  some  days,  during  which  the  contents  of  the 
alimentary  canal  must  have  been  changed  many  times, 
but  no  perceptible  effect  was  produced.  This  result 
also  serves  to  show  that  the  influences  act  very  slowly, 
and  that  the  processes  of  adjustment  are  totally  dif- 
ferent from  those  which  cause  the  rapid  changes  of 
colour  considered  in  Chapter  VII. 


154  THE  COLOUKS  OF 


The  difference  between  slow  and  rapid  adjustment 
of  colour 

The  essential  difference  between  the  two  kinds  of 
adjustment  is  that,  in  the  one  case,  the  pigmented 
part  of  certain  cells  contracts  in  obedience  to  nervous 
stimuli,  and  thus  alters  the  general  appearance  ;  while 
in  the  other  case  the  coloured  part  is  actually  built 
up  of  the  appropriate  tint,  or  loses  its  colour  alto- 
gether and  becomes  transparent  in  obedience  to  the 
same  stimuli.  The  frog  or  fish  has  a  series  of  ready- 
made  screens  which  can  be  shifted  to  suit  the  environ- 
ment ;  the  insect  has  the  power  of  building  up  an 
appropriate  screen.  In  many  cases,  however,  the 
green  colour  of  caterpillars  is  due  to  the  ready-made 
colour  of  the  blood,  which  becomes  effective  when 
pigment  is  removed  from  the  superficial  cells,  but 
which  disappears  when  the  latter  are  rendered 
opaque.  Here,  however,  the  superficial  cells  form  the 
screen  which  has  to  be  built  up  or  from  which  the 
colour  must  be  dismissed ;  and  in  certain  species 
even  the  colour  of  the  blood  is  entirely  changed  in 
the  passage  from  a  green  to  a  dark  variety  or  vice 
versa. 

Hence  it  is  to  be  expected  that  the  changes  occur- 
ring in  an  insect  will  occupy  a  considerable  time  as 
compared  with  those  which  take  place  in  a  frog. 
Another  difference  between  the  two  processes  is  that 


VARIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    155 

the  stimulus  from  the  environment  falls  upon  the  eye 
in  the  one  case  and  probably  upon  the  surface  of  the 
skin  in  the  other. 


Variable  Protective  Resemblance  in  insects  is  no 
explanation  of  the  origin  of  colour 

Many  authorities  have  believed  that,  in  the  results 
of  these  experiments  upon  the  colours  of  insects,  we 
see  an  explanation  of  the  origin  of  colour,  by  the  direct 
influence  of  environment  accumulated  through  many 
generations.  This  is  a  very  tempting  conclusion,  and 
one  which  for  a  time  appeared  to  me  to  be  satisfactory. 
But  as  soon  as  there  was  clear  evidence  that  the 
medium  of  the  nervous  system  is  necessary,  the 
results  were  seen  to  be  indirect,  and  to  have  needed 
the  most  astonishing  adaptations  on  the  part  of  the 
organism  before  the  colour  of  the  environment  could 
exercise  any  influence  upon  it. 

It  might  still  be  maintaine'd  that  the  existing 
colours  and  markings  of  certain  caterpillars  are  at  any 
rate  in  part  due  to  the  accumulation  through  heredity 
of  the  indirect  influence  of  environment,  working  by 
means  of  the  nervous  system.  To  this  it  may  be 
replied  that  the  whole  use  and  meaning  of  the  power 
of  adjustment  depends  upon  its  freedom  during  the  life 
of  the  individual ;  any  hereditary  bias  towards  the 
colours  of  ancestors  would  at  once  destroy  the  utility 
of  the  power,  which  is  essentially  an  adaptation  to  the 


156  THE  COLOURS  OF  ANIMALS 

fact  that  different  individuals  will  probably  meet  with 
different  environments.  As  long  ago  as  1873,  Pro- 
fessor Meldola  argued  that  this  power  of  adjustment 
is  adaptive  and  to  be  explained  by  the  operation  of 
natural  selection.1 

Comparison  between  the  varying  effects  of  green 
leaves  upon  the  different  stages  of  an  insect  strongly 
supports  the  view  that  the  results  are  due  to  adaptation. 
Thus  the  caterpillar  of  the  Brimstone  Moth  remains 
upon  its  food-plant  for  a  few  weeks  in  the  summer  when 
the  leaves  are  green,  and  green  leaves  cause  the  larva 
to  become  green  and  to  lose  the  dark  pigment.  But 
the  chrysalis  remains  among  the  leaves  in  winter 
when  they  have  become  brown,  and  green  leaves  cause 
the  caterpillar  to  spin  a  dark  cocoon.  Hence  precisely 
opposite  effects  are  produced  by  the  operation  of  the 
same  force,  the  nature  of  the  effects  having  been 
determined  by  adaptation. 

Furthermore,  there  is  no  positive  evidence  for  any 
of  these  effects  becoming  hereditary.  I  have  carried 
on  some  of  my  experiments  for  more  than  one  genera- 
tion, always  carefully  noting  the  effects  produced  in 
the  parents,  and  have  never  been  able  to  detect  any 
resulting  hereditary  tendencies,  even  when  the  previous 
generation  had  been  powerfully  influenced. 

When  therefore  we  meet  with  a  dimorphic  species 
which  is  not  influenced  by  its  environment,  so  as  to 
produce  the  appropriate  form,  I  do  not  believe  that  we 

'  Proc.  Zool.  Soc.  1873,  p.  153. 


VAKIABLE  PROTECTIVE  RESEMBLANCE  IN  INSECTS    157 

are  witnessing  the  results  of  a  power  of  adjustment 
which  existed  in  the  past  but  is  now  lost.  I  think,  on 
the  other  hand,  that  variability  or  dimorphism  pre- 
ceded the  power  of  adjustment  in  all  cases.  I  have 
already  shown  that  these  appearances  possess  a  pro- 
tective value  even  when  they  cannot  be  adjusted  (see 
pp.  46-48).  When  Variable  Protective  Eesemblance  is 
present,  but  acts  somewhat  uncertainly  (as  in  the  larva 
of  the  Eyed  Hawk  Moth),  it  is  probable  that  the  power 
has  been  only  recently  acquired  and  is  still  imper- 
fect. This  conclusion  is  supported  by  the  fact  that 
the  closely  allied  caterpillar  of  the  Convolvulus  Hawk 
Moth  (Sphinx  convolvuli)  has  no  power  of  adjustment, 
although  it  is  completely  dimorphic 1  (see  pp.  47,  48). 
Before  finally  leaving  this  part  of  the  subject  I 
will  briefly  allude  to  facts  which  render  it  probable  that 
certain  perfect  insects  possess  the  power  of  Variable 
Protective  Eesemblance. 


Variable  Protective  Resemblance  probable  in  certain 
Moths 

The  colour  of  certain  insects  varies  with  the  pre- 
vailing tint  of  the  locality  in  which  they  occur.  The 
best  instance  known  to  me  is  that  of  one  of  the 
Geometrce,  the  Annulet  Moth  (Gnophos  obscurata). 
This  moth  is  light-coloured  in  chalky  localities  (e.g. 
on  the  chalk  at  Lulworth),  but  darker  when  the  pre- 

1  Trans.  Ent.  Soc.  Land.  1888,  pp.  552-553. 


158  THE  COLOUES  OF  ANIMALS 

vailing  tint  of  the  earth  is  dark,  as  in  peaty  districts. 
It  is  improbable  that  these  are  local  races,  and  the 
only  other  interpretation  is  that  the  colours  can  be 
varied  as  the  result  of  a  stimulus.  No  experimental 
proof  of  this  has  been  as  yet  afforded.  If  the  view 
adopted  here  be  correct,  it  will  be  of  extreme  interest 
to  define  the  susceptible  period ;  it  will  most  probably 
be  found  at  the  close  of  larval  life. 

I  have  treated  this  part  of  the  subject  at  some 
length  and  have  discussed  many  details.  I  have  done 
so  because  the  inquiry  is  new,  and  will  not  be  found 
in  other  books  on  the  colours  of  animals ; l  and  also 
because  I  hope  that  some  of  my  readers  may  be  in- 
duced to  carry  on  investigations  for  themselves  in  a 
field  which  is  easily  entered,  and  in  which  further 
help  is  especially  necessary. 

1  Since  this  sentence  was  written,  Mr.  A.  B.  Wallace's  most  inter- 
esting volume,  Darwinism,  has  appeared.  A  short  account  of  Variable 
Protective  Resemblance  in  insects  will  be  found  in  it. 


CHAPTEE  X 

WARNING   COLOURS 

WE  now  come  to  a  class  of  colours  with  a  meaning 
precisely  opposite  to  that  of  the  large  class  we  have 
just  been  considering.  The  object  of  the  latter  is  to 
conceal  the  possessor  from  its  enemies,  the  object  of 
the  former  is  to  render  it  as  conspicuous  as  possible. 
As  in  other  classes  of  colour,  the  most  familiar  and 
striking  illustrations  are  to  be  found  among  insects.1 

The  sharp  contrast  between  most  Protective  or  Aggres- 
sive Resemblances  and  Warning  Colours 

It  must  have  been  obvious  to  any  one  interested  in 
natural  history  that  the  insects  met  with  during  a 
walk  in  summer  may  be  arranged  in  two  great  groups  : 
those  which  are  extremely  difficult  to  find  and  excite 
our  wonder  by  the  perfect  manner  in  which  they  are 
concealed,  and  those  which  at  once  attract  our  attention 
by  their  startling  colours  and  conspicuous  attitudes, 
the  effect  being  often  greatly  increased  by  the  habit 

1  Many  of  the  facts  and  conclusions  in  this  chapter  are  taken  from 
my  paper  in  the  Proc.  Zool.  Soc.  1887,  p.  191. 


160  THE  COLOURS  OF  ANIMALS 

of  living  in  companies.  These  two  groups  form, 
perhaps,  the  sharpest  contrast  in  nature.  We 
assume,  almost  as  a  matter  of  course,  that  the  latter 
are  protected  in  some  other  way,  that  if  captured 
they  would  prove  to  be  of  little  value,  or  even  posi- 
tively nauseous  or  dangerous. 


The  value  of  Warning  Colours 

At  first  sight  the  existence  of  this  group  seems  to 
be  a  difficulty  in  the  way  of  the  general  applicability 
of  the  theory  of  natural  selection.  Warning  Colours 
appear  to  benefit  the  would-be  enemies  rather  than 
the  conspicuous  forms  themselves,  and  the  origin  and 
growth  of  a  character  intended  solely  for  the  advan- 
tage of  some  other  species  cannot  be  explained  by  the 
theory  of  natural  selection.  But  the  conspicuous 
animal  is  greatly  benefited  by  its  Warning  Colours. 
If  it  resembled  its  surroundings  like  the  members 
of  the  other  class,  it  would  be  liable  to  a  great  deal  of 
accidental  or  experimental  tasting,  and  there  would 
be  nothing  about  it  to  impress  the  memory  of  an 
enemy,  and  thus  to  prevent  the  continual  destruction 
of  individuals.  The  object  of  Warning  Colours  is 
to  assist  the  education  of  enemies,  enabling  them  to 
easily  learn  and  remember  the  animals  which  are  to 
be  avoided.  The  great  advantage  conferred  upon  the 
conspicuous  species  is  obvious  when  it  is  remembered 
that  such  an  easy  and  successful  education  means  an 


WARNING  COLOUES  161 

education  involving  only  a  small  sacrifice  of  life.  It 
must  not  be  supposed  that  nauseous  properties  are 
necessarily  attended  by  Warning  Colours  ;  there  are 
very  many  instances  in  which  they  are  accompanied 
by  Protective  Kesemblances  and  habits.  The  common 
cockroach  is  a  familiar  example  of  this  latter  asso- 
ciation. 

Warning  Colours  in  Mammalia 

The  highest  vertebrate  animals  are  rarely  protected 
by  the  possession  of  the  qualities  which-are  most  com- 
monly attended  by  Warning  Colours,  viz.  an  unplea- 
sant taste  or  smell.  There  is,  however,  at  least  one 
mammal  of  which  this  is  certainly  true.  This  ex- 
ample is  brought  forward  hi  Belt's  most  interesting 
book,  '  The  Naturalist  in  Nicaragua.' l  Thus  he  tells 
us  that  at  night  '  the  skunk  goes  leisurely  along, 
holding  up  his  white  tail  as  a  danger- flag  for  none  to 
come  within  range  of  his  nauseous  artillery.'  He  also 
alludes  to  the  fetid  fluid  which  these  animals '  discharge 
with  too  sure  an  aim  at  any  assailant.'  He  describes 
the  large  white  tail  as  laid  over  against  the  black  and 
white  body,  producing  a  very  conspicuous  effect  in 
the  dusk,  so  that  the  animal  '  is  not  likely  to  be 
pounced  upon  by  any  of  the  Carnivora,  mistaking  it 
for  other  night-roaming  animals.'  The  conspicuous 
appearance  of  the  skunk  is  shown  in  fig.  42. 

1  Second  edition,  1888,  pp.  174,  249,  250,  320,  321.  See  also 
Mr.  A.  E.  Wallace's  Darwinism,  1st  edition,  p.  233. 


162 


THE  COLOURS  OF  ANIMALS 


I  know  of  no  instance  of  this  kind  among  birds,  but 
it  is  probable  that  the  gaudy  and  strongly-contrasted 
colours  of  certain  tropical  species  may  be  found  to  be 
accompanied  by  some  nauseous  property  and  to  be  of 
warning  significance. 


RG.  42. — The  Brazilian  Skunk  (Afephiti*  suffocant)  :  showing  the  conspicuous  black 
and  white  appearance  of  the  animal  which  serves  as  a  warning  to  its  enemies. 

The  brilliant  and  conspicuous  colours  of  many 
powerful  birds  are,  I  think,  to  be  explained  as  a 
result  of  the  free  scope  given  to  sexual  selection  (see 
pp.  311-12). 


WAENING-  COLOURS  163 


Warning  Colours  in  Reptiles 

Warning  characters  are  not  uncommon  among 
poisonous  reptiles.  The  various  species  of  Coral 
Snake  (Elaps),  occurring  in  tropical  America,  are  ex- 
tremely venomous,  and  are  highly  conspicuous,  their 
bodies  being  alternately  banded  with  bright  red  and 
black,  and  often  with  yellow.1  It  is  extremely  in- 
teresting to  observe  that  the  deadly  Eattlesnake 
(Crotalus)  warns  an  intruder  of  its  presence  by  sound 
instead  of  by  sight,  like  the  Coral  Snake.  The  Cobra 
is  protectively  coloured,  but,  if  attacked,  it  expands 
the  hood  with  the  conspicuous  eye-like  marks,  and 
thus  endeavours  to  terrify  its  enemy  by  the  startling 
appearance.  The  majority  of  poisonous  snakes,  how- 
ever, depend  entirely  upon  Protective  Resemblance 
together  with  the  use  of  their  fangs.  This,  for  ex- 
ample, is  the  case  with  our  common  Viper. 

It  is,  however,  an  advantage  to  some  snakes  to 
acquire  warning  characters  and  to  live  on  their  repu- 
tation for  being  poisonous;  for  although  an  animal 
bitten  by  one  of  them  would  probably  die,  the  effects 
are  never  immediately  fatal,  and  there  would  be  plenty 
of  time  for  the  snake  itself  to  be  killed.  Again,  the 
snake  possesses  only  a  limited  supply  of  poison  at  any 
one  time,  and  if  this  had  been  recently  drawn  upon 

1  See  also  A.  B.  Wallace's  Essays  on  Natural  Selection,  1875, 
p.  101. 


164  THE  COLOUES  OF  ANIMALS 

for  purposes  of  defence  or  for  killing  prey,  the  snake 
would  be  comparatively  harmless.  Hence  it  .would 
be  to  the  advantage  of  certain  snakes  to  advertise 
publicly  the  fact  that  they  are  dangerous,  retaining 
the  poison  to  use  if  necessary ;  and  others  would  gain 
by  concealing  themselves  by  Protective  Eesemblance, 
while  they  also  would  use  their  poison  fangs  if  detected 
and  attacked.  The  question  is  not  whether  one  of 
these  methods  is  better  than  the  other,  but  whether 
either  of  them  is  better  than  an  intermediate  con- 
dition ;  so  that  we  can  well  understand  why  one 
group  of  poisonous  snakes  should  adopt  one  method, 
while  the  other  method  is  made  use  of  by  another 
group. 

Warning  Colours  in  Amphibia 

Among  the  Amphibia  a  beautiful  example  has  been 
afforded  by  Mr.  Belt's  acute  powers  of  observation.1 
'  In  the  woods  around  Santo  Domingo  there  are  many 
frogs.  Some  are  green  or  brown,  and  imitate  green 
or  dead  leaves,  and  live  amongst  foliage.  Others  are 
dull  earth-coloured,  and  hide  in  holes  and  under  logs. 
All  these  come  out  only  at  night  to  feed,  and  they  are 
all  preyed  upon  by  snakes  and  birds.  In  contrast 
with  these  obscurely  coloured  species  another  little" 
frog  hops  about  in  the  daytime,  dressed  in  a  bright 
livery  of  red  and  blue.  He  cannot  be  mistaken  for 
any  other,  and  his  flaming  vest  and  blue  stockings 

'  Loc.  tit.  p.  32L 


WARNING  COLOURS  165 

show  that  he  does  not  court  concealment.  He  is  very 
abundant  in  the  damp  woods,  and  I  was  convinced  he 
was  uneatable  so  soon  as  I  made  his  acquaintance 
and  saw  the  happy  sense  of  security  with  which  he 
hopped  about.  I  took  a  few  specimens  home  with  me 
and  tried  my  fowls  and  ducks  with  them,  but  none 
would  touch  them.  At  last,  by  throwing  down  pieces 
of  meat,  for  which  there  was  a  great  competition 
amongst  them,  I  managed  to  entice  a  young  duck  into 
snatching  up  one  of  the  little  frogs.  Instead  of  swal- 
lowing it,  however,  it  instantly  threw  it  out  of  its 
mouth,  and  went  about  jerking  its  head,  as  if  trying 
to  throw  off  some  unpleasant  taste.'  It  is  also  ex- 
tremely probable  that  the  well-known  European  Sala- 
mander (Salamandra  maculosd),  so  conspicuous  with 
its  irregular  yellow  blotches  on  a  black  ground,  pos- 
sesses some  unpleasant  attribute.  I  do  not  think, 
however,  that  there  is  any  direct  evidence  for  this, 
like  that  obtained  by  Mr.  Belt  in  the  case  of  the 
Nicaraguan  frog. 

Warning  Colours  in  Marine  Animals 
Many  fish  are  poisonous,  and  many  possess  for- 
midable defensive  spines,  but  I  do  not  know  that  any 
attempt  has  been  made  to  connect  these  characters 
with  a  conspicuous  appearance.  It  is  very  probable, 
however,  that  such  a  connection  exists  in  many  cases.1 

1  Mr.  Garstang  suggests  that  the  weever-fish  (Trachinus  viper  a) 
is  an  example  of  Warning  Colouration.    It  possesses  a  pair  of  in- 


166         THE  COLOUES  OF  ANIMALS 

"Warning  Colours  are  probably  wide-spread  among 
marine  organisms.  Mr.  Garstang  had  suspected  that 
the  bright  colours  of  certain  compound  Ascidians  were 
of  warning  significance,  because  these  helpless  animals 
are  thus  rendered  extremely  conspicuous,  and  because 
some  of  them  emit  a  most  unpleasant  odour.  He  now 
finds  that  fish  invariably  refuse  them  :  although  some- 
times tasted  or  even  swallowed,  they  are  never  retained. 
The  bright  colours  of  many  sea-antmones  and  sponges 
are  probably  to  be  explained  in  the  same  way.  Evi- 
dence in  favour  of  this  conclusion  is  given  on  pp. 

200-204. 

( 

Warning  Colours  in  Caterpillars  :  the  history  of  their 
discovery 

Warning  Colours  are  greatly  developed  in  insects, 
and  an  account  of  the  first  recognition  of  this  prin- 
ciple among  caterpillars  is  of  great  historical  interest. 
When  Darwin  was  investigating  the  bright  colours  of 
animals,  and  was  elaborating  his  theory  of  their  ex- 
planation as  of  use  in  courtship,  he  came  across  the 
brilliant  colours  of  certain  caterpillars,  and  saw  at 

tensely  poisonous  spines  on  its  gill-covers,  and  is  rendered  conspicuous 
by  a  deep  black  first  dorsal  fin.  The  body  of  the  fish  is  completely 
buried  in  the  sand,  which  it  resembles  in  colour,  the  black  fin  alone 
being  seen.  Mr.  Garstang  thinks  that  this  conspicuous  character 
prevents  such  fish  as  gurnards  from  mistaking  the  weever  for  the 
dragonet  (Callionymus  lyra),  which  is  similar  in  size  and  habits.  He 
has  frequently  found  the  dragonet  in  the  stomachs  of  gurnards,  but 
the  weever  never. 


WARNING-  COLOURS  167 

once  that  they  were  a  difficulty  in  the  way  of  the 
theory.  For  caterpillars  are  undeveloped  organisms ; 
they  have  been  described  as  '  embryos  leading  an  in- 
dependent life,'  and  there  is  no  way  of  distinguishing 
the  sexes  by  external  colour  or  structure  (except  in  a 
few  instances).  Here,  therefore,  we  meet  with  bril- 
liant colours,  often  rendering  the  possessors  con- 
spicuous, which  cannot  be  of  any  use  in  courtship. 
Seeing,  therefore,  that  the  bright  colours  must  be  of 
use  in  some  other  way,  Darwin  drew  the  attention  of 
Wallace  to  the  subject,  and  asked  whether  he  could 
suggest  any  explanation.  Wallace  accordingly  thought 
over  the  subject,  and  considered  it  as  part  of  the 
wider  question  of  the  varied  uses  (other  than  sexual) 
of  brilliant  and  startling  colour,  in  other  stages  of 
insect-life,  and  in  numerous  instances  scattered  over 
the  whole  animal  kingdom ;  and  he  finally  ventured 
to  predict  that  birds  and  other  enemies  would  be  found 
to  refuse  such  conspicuous  caterpillars  if  offered  to 
them.  He  believed,  in  fact,  that  such  larvae  are  pro- 
tected by  possessing  a  nauseous  taste  or  smell,  or  some 
other  property  which  renders  them  unfit  for  food. 
Conversely  Wallace  argued  that  inconspicuous  cater- 
pillars would  be  eaten  and  relished  whenever  they 
were  detected. 

It  is  most  inspiring  to  read  the  letter  in  which  the 
great  founder  of  modern  biology  accepted  this  fruitful 
suggestion. 

'  .  .  .  You  are  the  man  to  apply  to  in  a  difficulty. 


168  THE  COLOUKS  OF  ANIMALS 

I  never  heard  anything  more  ingenious  than  your 
suggestion,  and  I  hope  you  may  be  able  to  prove  it 
true.  That  is  a  splendid  fact  about  the  white  moths ; 
it  warms  one's  very  blood  to  see  a  theory  thus  almost 
proved  to  be  true.'1 

Very  soon  after  the  suggestion  was  made  public 2 
it  received  confirmation  by  experiments  conducted  by 
Mr.  J.  Jenner  Weir 3  and  Mr.  A.  G.  Butler.4  At  a 
later  date  experiments  of  the  same  kind  were  made  by 
Professor  Weismann,5  and  still  later  by  myself.6  It 
was  found  that  while  birds  devoured  with  eagerness 
the  well-concealed  caterpillars,  they  refused  those 
with  conspicuous  colours;  it  was  also  found  that 
other  insect-eating  animals,  such  as  frogs,  lizards, 
and  spiders,  refused  larvae  with  warning  colours,  or 
did  so  after  first  tasting  them. 


Examples  of  Warning  Colours  among  Caterpillars 

A  very  common  example  of  a  caterpillar  with 
warning  colours  is  afforded  by  the  larva  of  the  Cur- 
rant Moth  or  Magpie  Moth  (Abraxas  grossulariata) , 
which  is  excessively  abundant  in  gardens  (see  fig.  43) 

1  Life  and  Letters  of  Charles  Darwin,  1887,  vol.  iii.  p.  94. 

2  Proc.  Ent.  Soc.  Lond.  Ser.  3,  v.  p.  Ixxx.  1867. 
»  Trans.  Ent.  Soc.  Lond.  1869,  Part  i.  April. 

*  Ibid.  p.  27. 

•  Studies  in  the  Theory  of  Descent,  Part  ii.  pp.  336-340.    English 
translation  by  Professor  B.  Meldola. 

6  Proc.  Zool.  Soc.  1887,  p.  191.  This  paper  contains  an  account 
of  all  previous  work  on  the  same  subject. 


WAENING  COLOURS 


169 


The  caterpillar  is  extremely  conspicuous,  being  of  a 
cream  colour  with  orange  and  black  markings.  Al- 
though it  belongs  to  the  group  of  well- 
concealed  '  stick-caterpillars '  (Geome- 
tm),  of  which  several  instances  have 
been  considered  in  Chapter  III.,  it  makes 
no  attempt  to  hold  itself  in  any  of  the 
attitudes  characteristic  of  its  group 
(compare  fig.  43  with  figs.  1,  2,  3,  4,  6, 
8,  and  9).  All  observers  agree  that 
birds,  lizards,  frogs,  and  spiders  either 
refuse  this  species  altogether,  or  exhibit 
signs  of  the  most  intense  disgust  after 
tasting  it. 


FIG.  43. — The  larva 
of  Magpie  Moth 
(A.  grosnulariata), 
showing  Warning 
Colouring ;  full- 
led ;  natural  size. 


PIG .  44.— The  larva  of  Buff-tip  Moth  (P.  Bucephala  ), 
showing  Warning  Colouring;  full-fed  ;  natural 
size ;  from  Curtis. 


FIG.  45.— The  larva  of  Cinnabar 
Moth  (E.  Jaeobcece),  showing 
Warning  Colouring ;  full-fed; 
natural  size ;  from  Curtis. 


170         THE  COLOURS  OF  ANIMALS 

The  caterpillar  of  the  Buff-tip  Moth  (Pygaera  bu- 
cephala),  fig.  44,  and  the  Cinnabar  Moth  (Euchelia 
jacobaa),  fig.  45,  are  also  extremely  abundant,  and 
are  good  examples  of  the  association  of  Warning 
Colours  with  a  nauseous  taste.  Both  of  them  are 
gregarious,  living  in  large  companies,  so  that  their 
conspicuous  appearance  is  greatly  intensified.  The 
colours  of  the  first-named  larva  are  black,  yellow,  and 
orange.  It  feeds  on  oak,  elm,  lime,  birch,  hazel,  &c., 
and  the  large  bare  branches  which  attest  its  appetite 
are  very  familiar  sights  in  autumn.  The  second 
caterpillar  is  coloured  by  alternate  black  and  yellow 
rings ;  it  feeds  upon  ragwort  in  the  summer.  There 
is  plenty  of  experimental  evidence  for  the  unpleasant 
taste  of  both  caterpillars. 

The  conspicuous  gregarious  caterpillars  of  the 
Large  Garden  White  Butterfly  (Pieris  brassicce),  which 
are  only  too  well  known  in  cabbage  gardens  in  the 
autumn,  are  also  protected  in  the  same  manner. 
Many  other  instances  will  be  found  in  the  papers 
already  referred  to. 

A  caterpillar  may  be  freely  exposed  rather  than 
conspicuous 

In  some  cases  the  warning  of  an  unpleasant 
quality  is  conveyed  by  the  caterpillar  being  freely 
exposed,  while  its  colours,  although  sober,  do  not 
harmonise  with  those  of  the  food-plant.  This  may 


WARNING  COLOURS  171 

be  true  of  gregarious  species,  such  as  the  dark  larvae  of 
the  Peacock  or  Small  Tortoiseshell  butterflies,  which 
feed  freely  exposed  on  the  tops  of  nettles,  and  which  are 
known  to  be  refused  by  some  insect-eating  animals.1 

The  various  unpleasant  qualities  possessed  by 
caterpillars  with  Warning  Colours 

Other  unpleasant  attributes,  as  well  as  that  of 
a  nauseous  taste,  may  be  associated  with  Warning 
Colours.  A  strongly  smelling  or  irritant  fluid  may  be 
discharged  from  special  glands  on  the  approach  of  an 
enemy.  Glands  of  this  kind  occur  on  the  back  of 
many  common  caterpillars,  such  as  the  brilliantly 
coloured  '  Palmer  worm  '  (larva  of  Porthesia  auriflua), 
or  the  onspicuous  '  Hop-dog '  (larva  of  Orgyia 
pudilunda).  The  larvae  of  some  common  gregarious 
saw-flies  (Hymenoptera),  such  as  Croesus  septentrionalis, 
which  completely  denudes  the  branches  of  birch  trees, 
have  a  number  of  odoriferous  glands  along  the  middle 
of  the  ventral  surface.  When  disturbed,  the  body  is 
turned  forward  over  the  head,  and  the  glands  are 
everted  so  that  their  secretion  escapes  into  the 
air.  The  meaning  of  the  gregarious  habit  is  very 

1  The  gregarious  habit  may  render  an  insect  so  conspicuous  that 
it  is  unnecessary  for  it  to  acquire  bright  colours.  The  '  warning  ' 
significance  of  the  gregarious  habit  was  first  suggested  by  Fritz 
Miiller  (Kosmos,  Dec.  1877).  An  abstract  of  this  paper  has  been 
published  by  Professor  Meldola  (Proc.  Ent.  Soc.  Lond.  1878,  pp.  vi. 
and  vii.) 


172  THE  COLOURS  OF  ANIMALS 

clear  in  this  and  parallel  cases  ;  for  when  many  indi- 
viduals combine  to  discharge  an  unpleasant  odour, 
they  become  surrounded  by  an  atmosphere  which  acts 
as  a  most  effective  barrier. 


Irritating  hairs  possessed  by  certain  larvae 

Again,  caterpillars  may  be  protected  by  possessing 
irritating  hairs.  This  is  the"  case  with  the  '  Palmer 
worms  '  mentioned  above,  which  are  thus  doubly  pro- 
tected. Many  people  have  discovered  this  fact  to 
their  cost  after  handling  these  pretty  black,  red,  and 
white  caterpillars,  which  are  so  abundant  and  freely 
exposed  on  our  hawthorn  hedges  in  early  summer. 
When  the  face  or  neck  is  touched  by  the  hands,  which 
are  covered  with  minute  barbed  hairs  shed  by  the 
caterpillar,  an  intensely  irritating  rash  soon  makes  its 
appearance.  The  same  effect  is  produced,  as  I  shall 
always  remember,  if  an  old  cocoon,  in  which  the  hairs 
are  interwoven,  be  pulled  to  pieces  with  the  fingers. 
These  caterpillars  were  nearly  always  refused,  but  Mr. 
Butler  records  that  they  were  in  one  case  eaten  with- 
out hesitation  by  a  young  sky-lark,  which  soon  after- 
wards died  with  symptoms  which  may  have  been  due 
to  the  irritating  hairs.  .  One  of  my  lizards  also  seized 
a  larva,  but  relinquished  it  after  biting  it  for  sometime. 
The  lizard  was  evidently  greatly  irritated  by  the  hairs 
in  its  mouth.  Many  other  hairy  caterpillars  also 
produce  a  rash :  thus,  the  larvae  of  the  Fox  Moth 


WARNING  COLOURS  173 

(Lasiocampa  rw&t),0ak  Eggar  (L.  quercus),  and  Drinker 
(Odonestis  potatorid),  have  this  effect  on  the  skin  of 
the  hands  if  they  are  held  for  a  long  time,  and  they 
would  certainly  act  rapidly  upon  the  delicate  skin  of 
the  mouth.  All  thre.e  caterpillars  are  fairly  con- 
spicuous, and  there  is  experimental  evidence  that  the 
two  latter  are  disliked. 

It  will  be  shown  that  the  hairs  are  sometimes 
arranged  in  tempting  tufts,  which  invite  an  enemy  to 
seize  the  caterpillar  at  a  point  which  does  not  injure 
the  latter,  while  it  causes  the  former  the  greatest  dis- 
comfort. 

The  hairs  of  nearly  all  caterpillars  are  probably 
more  or  less  unpleasant  in  the  mouth.  Delicate  and 
sensitive  animals,  such  as  the  marmoset,  although  ex- 
cessively fond  of  insects,  cannot  be  induced  to  touch 
any  hairy  larva.  Birds  appear  to  eat  them  more 
readily  than  other  animals,  but  they  have  peculiar 
advantages  in  their  power  of  rubbing  off  the  hairs. 

The  association  of  hairs  with  a  conspicuous  appearance 

Sir  John  Lubbock l  has  tabulated  the  appearance 
of  the  larvae  of  all  British  butterflies  and  the  larger 
moths,  and  he  thus  shows  in  a  most  convincing 
manner  the  general  association  of  hairs  or  spines  with 
conspicuous  warning  colours.  His  conclusion  is  as 
follows :  '  Thus  summing  up  the  caterpillars,  both  of 

1  Trails.  Ent.  Soc.  1878,  pp.  239,  et  sej. 
9 


174         THE  COLOURS  OF  ANIMALS 

the  butterflies  and  moths,  out  of  the  eighty-eight  spiny 
and  hairy  species  tabulated  only  one  is  green  (L. 
syUlla),  and  even  this  may  not  be  protectively  coloured, 
since  it  has  yellow  warts  and  white  lateral  lines.  On 
the  other  hand,  a  very  great  majority  of  the  "alack  and 
brown  caterpillars,  as  well  as  those  more  or  less 
marked  with  blue  and  red,  are  either  hairy  or  spiny, 
or  have  some  special  protection.'  ) 

Sir  John  Lubbock,  however,  fully  recognises  that 
hairs  may  contribute  towards  tb£  Protective  Eesem- 
blance  of  certain  species,  examples  of  which  have 
been  already  given  (see  page  35).  Professor  Meldola 
suggests  that  a  probable  original  meaning  of  the  hairy 
covering  was  protection  from  injury  after  falling  from 
the  food-plant. 


Warning  Colours  in  other  stages  of  metamorphosis  in 
Lepidoptera 

Lepidoptera  of  many  species  are  protected  by 
Warning  Colours  and  unpleasant  attributes,  in  other 
stages  in  addition  to  that  of  the  larva ;  and  the  same 
method  of  defence  is  also  adopted  in  other  orders  of 
insects.  The  chrysalis  of  the  Magpie  Moth,  which  is 
black  with  yellow  bands,  and  exposed  to  view  in  a  very 
slight  cocoon,  is  nauseous  like  the  larva,  and  the  slow- 
flying  moth  itself,  with  white  wings  rendered  conspicu- 
ous by  yellow  markings  and  black  spots,  is  defended  in 
the  same  manner.  When  captured  it  makes  no  attempt 


WARNING   COLOURS  175 

to  escape,  but  '  feigns  death.'  The  conspicuous  and 
sluggish  day -flying  black  and  red  Burnet  Moths 
(Zygcena)  and  Cinnabar  Moth  (Euchelia  Jacobcece)  are 
also  nauseous,  and  so  is  the  gaudy  Garden  Tiger  Moth 
(Arctia  caja).  Many  white  moths,  or  black  and  white 
moths,  have  also  been  refused  by  insect-eating  animals 
with  every  sign  of  disgust. 


Consideration  of  the  later  stages  of  species  with 
unpalatable  larv» 

A  comparison  of  the  means  of  defence  and  palata- 
bility  in  the  three  stages  of  metamorphosis,  in  species 
of  which  the  larvae  are  known  to  be  nauseous,  proved  to 
be  extremely  interesting,  and  much  more  work  is  needed 
in  the  same  direction.  In  the  first  place  the  com- 
parison showed  that  when  the  later  stages  are  nauseous 
the  larva  was  also  nauseous  in  all  cases.  The  Tiger 
Moth  is  probably  an  exception,  for  the  caterpillar  may 
be  defended  by  its  hairs  instead  of  by  taste,  and  the 
chrysalis  seems  to  be  palatable.  The  Leopard  Moth 
(Zeuzera  cesculi]  is  another  exception.  Such  cases  are 
probably  very  rare,  and  it  is  clear  that  this  method  of 
defence,  among  Lepidoptera,  nearly  always  arose  in 
the  larval  stage.  The  larval  stage  is  exposed  to  more 
danger  and  is  more  helpless  than  any  other :  the 
imago  can  escape  by  flight,  and  the  pupa,  if  exposed, 
may  render  its  Protective  Resemblance  complete  by 
entire  quiescence,  and  it  is  usually  effectually  protected 


176         THE  COLOURS  OF  ANIMALS 

in  other  ways.  But  the  larva  must  feed,  and  at  the 
same  time  is  sluggish  in  its  movements,  defenceless, 
and  when  palatable  is  more  relished  than  any  other 
stage,  for  it  does  not  possess  the  hard  investment  of 
the  one  or  the  scaly  covering  of  the  other.  Hence  it 
is  that  the  great  needs  of  the  larva  have  been  so  fre- 
quently met  in  this  way;  but  as  soon  as  the  un- 
pleasant quality  has  appeared  it  will  tend  to  pass  on 
by  simple  continuity  into  the  other  stages.  If  these 
latter  are  hard  pressed,  there  is  always  the  possibility 
that  such  qualities  may  be  made  the  starting-point  of 
a  similar  method  of  defence  for  them  also.  But  the 
disagreeable  properties  may  also  pass  on  into  stages 
which  hold  their  own  successfully  by  elaborate  and 
perfect  Protective  Eesemblances,  and  then  such  quali- 
ties, unattended  by  Warning  Colours,  are  entirely  use- 
less to  the  stage,  but  may  be  important  as  a  latent 
possibility  for  the  future.  It  must  be  remembered 
that  an  unpleasant  attribute  must  always  appear  in 
advance  of  the  warning  colouring.  An  example  is 
afforded  by  the  Buff-tip  Moth  (Pygcera  Imcephala), 
which  is  beautifully  protected,  during  rest,  by  resem- 
bling a  piece  of  rotten  lichen -covered  stick  (see  page 
57),  but  which  nevertheless  retains  something  of  the 
unpleasant  taste  by  which  its  caterpillar  is  effectually 
protected. 


WARNING  COLOUKS  177 

The  metallic  appearance  of  certain  pupae  may  be  of 
value  as  a  warning 

At  this  point  it  is  of  interest  to  consider  the  cases 
in  which  the  metallic  appearance  of  a  chrysalis  may 
act  as  a  warning.  Dr.  Fritz  Miiller  tells  me  that  the 
brilliant  metallic  pupae  of  the  South  American  butter- 
fly, Mechanitis  lysimnia,  hang  in  groups  from  the 
leaves  of  their  food-plant  (Solanum).  The  butterfly  of 
this  species  is  certainly  distasteful,  for  the  genus  is 
mimicked  by  butterflies  of  other  families.  This  fact, 
and  the  gregarious  habit  of  the  pupae,  render  it  nearly 
certain  that  the  glittering  appearance  has  a  warning 
significance.  The  same  is  probably  true  of  the  pupa 
of  the  abundant  Indian  butterfly  (Euplcsa  core),  which 
Mr.  E.  A.  Minchin  tells  me  possesses  a  brilliant  silvery 
appearance,  and  is  so  conspicuous  that  it  can  be  seen 
from  a  great  distance.  This  butterfly  also  belongs  to 
a  group  protected  by  an  unpleasant  taste  or  smell, 
and  there  is  little  doubt  that  the  metallic  appearance 
of  the  pupa  has  a  warning  meaning. 

Warning  Colours  in  other  orders  of  Insects 

Passing  now  to  the  other  orders  of  insects,  highly 
conspicuous  and  abundant  beetles  (Coleoptera),  such 
as  the  black  and  red  '  soldiers  and  sailors '  (Tele- 
phorus],  the  red  and -black  ladybirds  (Coccinella),  and 
the  red  and  blue-black  Chrysomela  populi,  have  been 


178  THE  COLOURS  OF  ANIMALS 

shown  to  be  extremely  nauseous,  and  the  two  latter 
emit  a  very  unpleasant  smell. 

The  sting  possessed  by  the  females  of  so  many 
Hymenoptcra  is  obviously  an  unpleasant  attribute, . 
rendering  the  insect  disagreeable  or  even  dangerous  to 
eat.  We  find  accordingly  that  stinging  insects  are 
often  rendered  conspicuous  by  warning  colours,  of 
which  the  contrasted  dark  and  yellow  bands  of  the 
Common  Wasp,  the  Hornet,  and  of  many  Humble 
Bees,  furnish  examples. 

Warning  Colours  are  also  to  be  found  in  other 
orders,  but  it  is  unnecessary  to  give  further  examples. 
They  will  be  recognised  in  numbers  in  any  country 
walk  during  the  summer,  although  the  experimental 
proof  of  the  co-existence  of  some  unpleasant  attribute 
is  still  wanting  in  a  large  proportion  of  the  cases. 

Warning  Colours  can  only  be  safely  adopted  by  a  small 
proportion  of  the  Insects  in  any  country 

The  acquisition  of  an  unpleasant  taste  or  smell, 
together  with  a  conspicuous  appearance,  is  so  simple 
a  mode  of  protection,  and  yet  apparently  so  absolutely 
complete,  that  it  seems  remarkable  that  more  species 
have  not  availed  themselves  of  it.  What  can  be  the 
principle  which  works  in  antagonism  to  such  a  mode 
of  protection?  Thinking  over  this  subject,  as  the 
result  of  a  lecture  upon  the  facts  and  conclusions 
already  described,1  it  appeared  probable  that  such  an 

1  Delivered  at  the  Royal  Institution  in  the  spring  of  1886. 


WARNING  COLOUES  179 

antagonistic  principle  would  be  found  in  the  too  com- 
plete success  of  the  method  itself.  If  a  very  common 
insect,  forming  the  chief  food  of  some  animal,  gained 
protection  in  this  way,  the  latter  might  be  forced  to 
devour  the  unpalatable  food  in  order  to  avoid  starva- 
tion. And  the  same  result  might  readily  be  brought 
about  if  a  scarce  and  hard-pressed  form  adopted  the 
same  line,  and  became  dominant,  after  ousting  many 
species  which  were  important  as  food.  If  once  an 
insect- eating  species  were  driven  to  eat  any  such 
insect  in  spite  of  the  unpleasant  taste,  it  would  gradu- 
ally come  to  devour  it  with  relish,  and  the  insect 
would  be  in  great  danger  of  extermination,  because 
of  its  conspicuous  appearance. 

If  this  reasoning  be  correct,  it  is  clear  that  the 
mode  of  defence  is  by  no  means  perfect,  and  that  it 
depends  for  its  success  upon  the  existence  of  relatively 
abundant  palatable  forms  ;  in  other  words,  its  employ- 
ment must  be  strictlv  limited. 


Absence  of  Warning  Colours  in  the  seasons  when 
Insect  life  is  scarce 

A  very  interesting  fact  in  support  of  this  argument 
is  the  entire  disappearance  of  all  insects  with  Warning 
Colours  during  the  seasons  when  insect  life  is  scarce, 
and  when  insect-eating  animals  are  hard  pressed  for 
food.  And  yet,  if  it  were  safe  to  rely  on  such  a  mode 
of  defence,  the  Warning  Colours  would  be  especially 


180  THE  COLOURS   OF  ANIMALS 

conspicuous  at  these  times,  when  all  the  tints  of  nature 
are  sombre  and  form  a  background  against  which  the 
Warning  Colours  would  stand  out  in  startling  contrast. 
Certain  species,  which  are  defended  in  this  way,  pass 
the  winter  in  the  brightly  coloured  stage  of  metamor- 
phosis ;  but  they  conceal  themselves  as  completely  as 
possible  under  loose  bark  or  among  dead  leaves,  &c. 
This  is  true  of  the  common  ladybird,  and  I  have 
noticed  that  they  begin  to  hide  comparatively  early  in 
the  autumn,  when  the  insects  are  rapidly  diminishing 
in  numbers,  but  before  the  beginning  of  the  cold 
weather.  It  is  therefore  probable  that  they  hide  in 
order  to  conceal  their  bright  colours  and  not  to  escape 
the  cold.-  It  is  also  known  that  ladybirds  are  eaten 
by  the  Green  Tree  frog  in  winter,  when  other  insect 
food  is  scarce,  and  also  by  hungry  birds,  although 
they  are  intensely  disliked  and  are  refused  (at  any  rate 
by  the  frogs)  if  other  food  can  be  obtained. 


Experimental  proof  that  Insect-eating  animals,  if 
hungry,  will  eat  unpalatable  species 

This  conclusion  was  tested  as  completely  as  pos- 
sible by  offering  conspicuous  unpalatable  insects  of 
many  species  to  animals  from  which  all  other  food 
was  withheld.  Under  these  circumstances  the  insects 
were  eaten,  although  often  after  many  attempts,  and 
evidently  with  the  most  intense  disgust. 


WARNING  COLOUES  181 


Natural  selection  has  enabled  certain  animals  to  eat 
unpalatable  Insects  with  apparent  relish 

Naturalists  have  always  recognised  that  an  insect 
may  be  distasteful  to  one  animal,  but  palatable  to 
another.  It  is,  however,  very  probable  that  these 
differences  have  been  acquired  comparatively  recently, 
and  have  arisen  out  of  the  competition  for  food.  In 
most  cases  the  change  of  habit  has  not  become  so  far 
confirmed  that  the  previously  distasteful  food  is  eaten 
with  avidity  and  pleasure.  Again,  when  we  find  that 
the  taste  of  an  insect  is  recognised  as  nauseous  by  a 
standard  wide  enough  to  include  mites  and  spiders  as 
well  as  birds,  lizards,  and  frogs,  it  appears  probable 
that  any  difference  of  opinion  is  due  to  an  altogether 
exceptional  immunity  conferred  upon  certain  species 
by  natural  selection. 

Nauseous  qualities  probably  do  not  affect  Insect 
parasites 

It  is  probable,  however,  that  this  argument  does 
not  apply  to  insect  parasites,  which  are  not  in  the 
position  to  gratify  their  tastes,  but  must  make  the 
best  of  the  larva  in  which  the  parent  has  deposited 
her  eggs.  It  is  clear  that  even  the  most  nauseous 
forms  must  suffer  greatly  from  the  attacks  of  enemies, 
for  the  average  number  of  individuals  in  each  species 
appears  to  remain  constant.  It  is  likely  that  the 


182         THE  COLOURS  OF  ANIMALS 

numbers  are  kept  down  by  special  liability  to  the 
attacks  of  insect  parasites,  in  one  or  more  stages. 
Thus  the  larva  of  the  Large  Garden  White  (Pieris 
brassicte)  is  known  to  be  nauseous,  but  the  im- 
munity from  attack  which  it  enjoys  by  no  means 
extends  to  its  insect  foes.  In  the  autumn  of  1888  I 
collected  some  hundreds  of  these  larvae  in  order  to 
experiment  upon  the  colours  of  their  pupaa.  I  ob- 
tained 109  pupae,  while  424  mature  larvae  died  from 
the  presence  of  the  parasitic  grubs  of  Ichneumon  flies 


The  likes  and  dislikes  of  Insect-eating  animals  are 
purely  relative 

It  may  be  taken  as  proved  that  the  continued 
spread  of  some  distasteful  form  and  the  correspond- 
ing diminution  of  edible  species  would  lead  to  the 
former  becoming  the  prey  of  insect-eating  animals  ; 
for  a  point  would  ultimately  be  reached,  as  it  was 
reached  in  many  of  my  experiments,  when  hunger 
would  become  a  stronger  stimulus  than  those  lesser 
prejudices  in  which  a  species  can  very  well  afford  to 
indulge  while  palatable  food  is  abundant.  These  pre- 
judices having  been  overcome  in  confinement,  there  is 
nothing  in  the  conditions  of  natural  life  which  could 
prevent  the  same  result  from  being  reached,  as  doubt- 
less it  has  been  reached  again  and  again.  The  com- 
parison of  all  experiments  of  this  kind  ever  made  with 
insects  will  show  that  the  likes  and  dislikes  of  insect- 


WARNING   COLOURS  183 

eating  animals  are  purely  relative,  and  are  manifested 
to  a  marked  extent  when  they  are  offered  a  variety 
of  insects,  and  when  obviously  nauseous  species  are 
excluded  from  the  list. 

Butterflies  and  moths  are  freely  eaten  by  lizards, 
but  they  are  not  enjoyed  like  houseflies  or  many  cater- 
pillars. This  is  probably  because  the  former  are  such 
dusty  and  unsatisfactory  things  to  eat,  with  such  a 
small  proportion  of  body  in  which  the  nutriment  and 
taste  is  contained,  and  so  large  an  expanse  of  dry 
membranous  wings  with  their  scaly  covering.  In 
this  respect  butterflies  contrast  unfavourably  with 
moths,  and  the  latter  are  certainly  greatly  preferred  by 
lizards  and  especially  birds.  The  latter  have  special 
advantages  in  being  able  to  pick  off  the  wings  before 
eating  the  body. 

In  the  excessive  abundance  of  insect-eating  ani- 
mals and  the  keen  competition  for  food  which  takes 
place,  we  see  the  conditions  which  must  render  the 
acquisition  of  an  unpleasant  taste  together  with  Warn- 
ing Colours  an  exceedingly  hazardous  mode  of  defence, 
if  assumed  by  more  than  a  small  proportion  of  the 
insects  of  a  country.  For  in  so  great  a  press  of  com- 
petition among  the  innumerable  insect-eaters,  we 
may  feel  sure  that  some  at  least  would  be  sufficiently 
enterprising  to  make  the  best  of  food  which  at  least 
has  the  advantage  of  being  easily  seen  and  caught. 

The  great  principle  of  Warning  Colours  has  de- 
servedly taken  a  most  important  place  among  the 


184  THE  COLOUES  OF  ANIMALS 

principles  which  deal  with  the  infinitely  complex  and 
ever-changing  relations  which  obtain  between  the 
most  widely  separated,  no  less  than  between  the  most 
closely  allied,  members  of  the  organic  kingdom.  But, 
nevertheless,  this  principle  carries  with  it  its  own 
compensating  principle,  which  will  come  into  opera- 
tion precisely  as  the  former  advances  to  the  possession 
of  undue  influence. 

The  education  of  enemies  assisted  by  the  fact  that 
Warning  Colours  and  patterns  often  resemble  each  other 

It  is  probably  unnecessary  for  the  young  insect- 
eating  animal  actually  to  make  trial  of  every  species 
of  nauseous  insect  in  its  locality,  in  order  to  be 
equipped  with  an  efficient  stock  of  experiences  with 
which  to  conduct  its  later  life.  Such  an  education 
would  be  somewhat  dearly  bought ;  it  would  be  un- 
pleasant to  the  insect-eater  and  destructive  to  the 
insect.  Since,  however,  the  same  colours  are  em- 
ployed again  and  again  by  unpalatable  or  dangerous 
insects  of  very  different  groups,  and  since  the  patterns 
are  also  frequently  repeated,  it  is  obvious  that  a  com- 
paratively few- unpleasant  experiences  would  be  suffi- 
cient to  create  a  prejudice  against  any  insect  with  a 
colour  or  pattern  at  all  resembling  the  nauseous  forms 
which  had  already  produced  BO  deep  an  impression 
upon  the  memory. 

This  conclusion  was  drawn  from  the  careful  com- 
parison of  the  colours  and  patterns  of  all  insects  which 


WAKNING  COLOURS  185 

have  been  experimentally  shown  to  be  distasteful. 
The  colours  which  produce  the  greatest  contrast,  and 
therefore  the  greatest  effect,  upon  the  eye  of  an  insect- 
eating  Vertebrate,  are  black  and  white,  and  next  to 
this  black  (or  some  very  dark  colour)  and  yellow, 
orange,  or  red ;  and  it  was  found  that  nearly  all 
unpalatable  or  dangerous  insects  were  coloured  with 
these  tints.  The  advantage  gained  by  the  acquisition 
of  such  colours  is  twofold  :  they  afford  the  combina- 
tions which  are  most  conspicuous  to  an  enemy,  and 
their  number  being  small,  while  nauseous  forms  are 
numerous,  the  continual  repetition  of  the  same  com- 
bination becomes  a  necessity,  and  this  also  facilitates 
the  education  of  enemies. 

There  are  similarly  a  few  eminently  conspicuous 
and  simple  patterns.  These  are — alternating  rings  of 
different  colours,  and  alternating  longitudinal  stripes, 
both  especially  suited  to  the  cylindrical  body-form, 
such  as  that  of  caterpillars,  &'c. ;  spots  upon  a  back- 
ground with  a  contrasted  colour,  especially  suited 
to  a  wide  expanse  such  as  the  wings  of  Lepidoptera. 
Every  insect  which  has  been  proved  to  be  distasteful 
was  found  to  possess  one  or  other  of  the  above  patterns 
or  some  combination  of  them.  Here  also  the  frequent 
similarity  of  the  patterns  of  nauseous  insects  is 
primarily  due  to  the  fact  that  there  is  only  a  limited 
number  of  appropriate  patterns,  but  also  because  the 
repetition  is  in  itself  advantageous  and  has  therefore 
been  encouraged  by  natural  selection. 


186  THE  COLOURS   OF  ANIMALS 

Some  of  the  advantages  of  true  mimicry  (to  be 
more  fully  described  below)  also  follow,  when  a  group 
of  insects  is  rendered  conspicuous  by  the  same 
colours  and  patterns,  and  when  certain  members  of 
the  group  are  noted  for  the  possession  of  especially 
unpleasant  attributes.  Thus  it  is  more  than  probable 
that  the  species  marked  by  alternate  rings  of  black 
and  yellow  (including  the  chrysalis  of  the  Magpie 
Moth  and  the  caterpillar  of  the  Cinnabar  Moth),  gain 
considerable  advantages  from  the  justly  respected 
appearance  of  Hornets  and  "Wasps.  It  must  not  be 
forgotten,  however,  that  the  latter  also  are  probably 
benefited,  although  to  a  much  smaller  extent,  by  the 
greater  publicity  which  follows  from  the  resemblance. 

The  causes  which  have  determined  the  resemblance 
between  Warning  Colours  in  different  Insects 

Hence  the  causes  which  determine  the  frequent 
repetition  of  the  same  colours  and  markings  in  dis- 
tasteful forms  are  as  follows:  (1)  The  fact  that  a 
limited  number  of  colours  and  patterns  are  especially 
efficient  in  attracting  the  attention  of  enemies,  and  in 
thus  facilitating  their  education;  (2)  the  fact  that 
the  education  of  enemies  is  also  rendered  easy  by 
requiring  them  to  learn  only  a  small  number  of  pat- 
terns and  colours ;  (3)  the  great  additional  advantage 
conferred  by  trading  upon  the  reputation  of  a  well- 
known  and  much-feared  or  much -disliked  insect. 


WAENING  COLOURS 


187 


The  warning  appearance  acquired  by  any  insect  is 
also  largely  determined  by  the  character  of  its  previous 
appearance,  which  formed  the  material  upon  which 
at  any  rate  the  first  steps  of  the  change  were  built. 

In  some  cases  we  can  successfully  read  the  history 
of  past  changes,  and  can  point  to  certain  parts  of  a 
warning  appearance  which  are  remnants  of  a  previous 
mode  of  defence  by  means  of  Protective  Eesemblance. 

Thus  the  orange  rings  of  the  caterpillar  of  the 
Cinnabar  Moth  harmonise 
well  with  the  flowers  of  its 
food  -  plant,  ragwort.1  The 
acquisition,  or  perhaps  only 
the  greater  prominence,  of 
the  strongly  contrasted  black 
bands,  and  above  all,  the 
gregarious  habits,  are  the 
later  developments  which  have 
followed  the  acquisition  of  an 
unpleasant  taste.  Again,  the 
caterpillars  of  the  Mullein 
Moth  (Cucullia  verbasci),  which 
are  so  abundant  and  con- 
spicuous on  various  species  of 
Mullein  (Verbascum) ,  are  even 
now  difficult  to  detect  when 
resting  among  the  dark  and 
yellow  sessile  flowers  studded  upon  the  surface  of  the 

1  First  noticed  by  T.  W.  Wood :  Insects  in  Disguise,  Student. 

isea 


FIG.  46.— Two  larvae  of  Mullein 
Moth  (Cucullia  verbasci)  on 
the  spike  of  the  Mullein ;  small 
in  last  stage  ;  natural  size. 


188  THE  COLOUES  OF  AOTVLAL9 

thick  green  spike  (see  fig.  46). !  The  conspicuous 
appearance  chiefly  depends  upon  the  gregarious 
habits,  and  upon  the  fact  that  the  larvse  com- 
monly rest  on  the  upper  surface  of  the  large  leaves, 
which  form  a  background  against  which  the  larval 


PIG.  47.—  Larva  of  Mullein  Moth  on  leaf  of  Mullein  ;  full-fed  ;  natural  siza 

colours  stand  out  with  startling  distinctness  (see  fig. 
47).  It  has  been  proved  that  these  larvae  possess  an 
unpleasant  although  not  an  extremely  nauseous  taste, 
so  that  here  also  we  have  evidence  that  the  change 
from  a  palatable  well-concealed  form  is  only  recent 
and  is  as  yet  incomplete. 


*  This  observation  w&s  ^o^^p^.tiDicfttod  to  Professor  ^kltddolci  by 
Mr.  Thomas  Eedle. 


CHAPTEE  XI 

WARNING  COLOURS   (continued) 

Sexual  colouring  may  be  made  use  of  for  warning 
purposes 

In  addition  to  the  modes  of  producing  a  warning 
appearance  which  we  have  hitherto  considered,  and 
which  are  almost  universal  in  this  country,  there  is 
another  method  which  is  very  conspicuous  in  the 
tropics.  In  certain  groups  of  mature  insects,  and 
especially  in  butterflies,  the  beautiful  colours  and 
patterns  which  have  been  produced  by  courtship, 
appear  to  have  been  made  use  of  as  an  indication  of 
some  unpleasant  quality. 

The  differences  between  Sexual  and  Warning  Colours 

The  tints  used  in  and  produced  by  courtship  are 
as  a  rule  easily  distinguished  from  Warning  Colours, 
even  when  both  occur  in  sexually  mature  insects. 
The  former  rarely  usurp  the  whole  surface  of  an  in- 
sect, and  they  are  carefully  concealed  during  repose. 
Thus  the  upper  sides  of  the  upper  wings  of  most 
moths,  and  the  under  sides  of  both  wings  in  butter- 


190         THE  COLOUES  OF  ANIMALS 

flies,  are  generally  protectively  coloured,  and  hide  the 
bright  colours  of  other  parts  when  the  insect  is  at 
rest.  If  the  parts  exposed  during  rest  are  conspicu- 
ously coloured  it  is  clear  that  they  chiefly  possess  a 
warning  significance.  I  say  '  chiefly,'  because  it  is 
probable  that  the  appearance  of  the  mature  individuals 
of  any  species,  however  much  it  may  be  specialised  for 
other  ends,  possesses  a  sexual  significance,  and  appeals 
as  an  adornment  to  the  modified  taste  of  the  individuals 
of  the  same  species.  We  have  a  rough  criterion  of 
the  extent  to  which  the  taste  has  been  modified  when 
we  compare  the  appearances  which  have  other  addi- 
tional meanings  with  those  which  possess  a  sexual 
value  alone,  and  which  are  concealed  except  during 
flight  and  are  especially  displayed  in  courtship. 
Warning  Colours  are  also  displayed  during  the  slug- 
gish flight  of  a  nauseous  species,  but  the  insects  with 
purely  ornamental  colours  are  swift  and  wary  when 
upon  the  wing. 

But  quite  apart  from  these  considerations,  the 
Warning  Colours  can  be  distinguished  by  the  subordi- 
nation of  every  other  feature  to  that  of  conspicuous- 
ness.  Crude  patterns  and  startling  strongly  contrasted 
colours  are  eminently  characteristic  of  a  warning 
appearance,  while  the  colours  and  patterns  produced 
by  courtship  include  everything  that  is  most  beautiful 
in  insects.  The  two  kinds  of  appearance  differ  as  an 
advertisement  differs  from  a  beautiful  picture:  the 
one  attracts  attention,  the  other  excites  admiration. 


WARNING  COLOURS  191 

The  transition  from  Sexual  to  Warning  Colours 

The  two  groups  nevertheless  run  into  each  other, 
and  a  beautiful  transition  is  afforded  by  the  insects 
in  which  sexually  produced  colours  and  patterns  are 
made  use  of  for  warning  purposes.  When  this  is  the 
case  the  colours  spread  on  to  the  parts  which  are  ex- 
posed during  rest,  and  the  flight  becomes  sluggish,  so 
that  they  are  displayed  as  completely  as  possible. 
These  are  the  insects  which  are  the  principal  models 
of  mimicry  in  tropical  countries,  and  Bates's  classical 
paper,  in  which  an  intelligible  theory  of  mimicry  was 
first  brought  forward,  deals  with  the  groups  which  are 
found  in  the  Amazon  valley,  and  with  the  forms  which 
resemble  them  and  share  the  advantages  conferred  by 
their  well-known  and  nauseous  qualities.  The  evi- 
dence for  the  existence  of  such  qualities  is  better 
considered  under  the  next  heading,  viz.  Mimicry. 

Resemblance  between  such  Warning  Colours  in  different 
species 

The  members  of  each  of  these  groups  resemble  one 
another  to  a  marked  extent ;  far  more  so  than  the 
species  of  other  groups  without  Warning  Colours. 
Thus  the  advantage  of  facilitating  the  education  of 
enemies  is  gained  by  them,  although  it  has  arisen  in  a 
manner  different  from  that  already  described  in  other 
unpalatable  insects  (see  pp.  184-86). 


192         THE  COLOUKS  OF  ANIMALS 

The  similarity  has  arisen  from  the  fact  that  the 
species  in  each  group  are  closely  related,  so  that 
natural  selection  has  maintained  an  initial  resem- 
blance, instead  of  causing  convergence,  as  it  has  done 
with  more  distantly  related  species.  Hence  repetition 
of  the  same  appearance  may  be  produced  by  a  pre- 
vented divergence,  as  in  these  cases,  or  by  the  actual 
convergence  of  forms  originally  unlike,  as  in  the  former 
cases. 

The  convergent  forms  are  more  perfectly  con- 
spicuous, more  ideally  warning,  because  they  have 
been  further  modified  from  their  original  appearance ; 
while  the  forms  in  which  divergence  has  been  arrested 
have  merely  adopted,  with  comparatively  slight  modi- 
fication, an  appearance  which  was  produced  by  the 
operation  of  other  principles,  but  which  is  sufficiently 
well  known  for  the  purpose. 

These  interesting  conclusions  have  gradually  grown 
out  of  the  observations  of  many  naturalists. 

The  arrested  divergence,  sometimes  aided  by  actual 
convergence,  has  produced  such  remarkable  resem- 
blances between  certain  species  of  unpalatable  insects, 
that  Bates  speaks  of  the  wonderful  fact  that  such 
species  mimic  each  other.  Wallace  at  first  looked 
upon  these  mysterious  resemblances  as  due  to  some 
unknown  cause  connected  with  locality,  for  the 
similar  species  are  nearly  always  found  together. 

The  difficulty  was  at  length  explained  by  Fritz 


WARNING  COLOURS  193 

Miiller.1  This  eminent  naturalist  suggested  that  both 
species  were  benefited  by  the  resemblance,  because 
the  number  of  individuals  which  must  be  sacrificed  to 
the  inexperience  of  young  birds  and  other  enemies 
would  be  made  up  by  both  of  them  instead  of  by  each 
independently.  This  fruitful  suggestion  was  at  once 
accepted  by  Wallace.2  The  mathematical  aspects  of 
the  subject  were  accurately  worked  out  by  Mr.  Blakis- 
ton  and  Mr.  Alexander,  of  Tokio,  Japan.3 

The  next  step  was  taken  by  Professor  Meldola,4 
who  extended  Fritz  Miiller's  explanation  of  these 
comparatively  rare  cases  of  close  resemblance,  to  the 
general  similarity  which  obtains  throughout  whole 
groups  of  unpalatable  and  conspicuous  species.  '  The 
prevalence  of  one  type  of  marking  and  colouring 
throughout  immense  numbers  of  species  in  protected 
groups,  such  as  the  tawny  species  of  Danais,  the 
barred  Heliconias,  the  blue-black  Euplceas,  and  the 
fibrous  Acrceas,  is  perfectly  intelligible  in  the  light  of 
the  new  hypothesis.' 

This  list  comprises  the  whole  of  the  large  groups 
of  butterflies  alluded  to  in  the  last  few  pages.  The 
species  belonging  to  them  are  very  familiar  in  every 
collection  of  tropical  butterflies,  while  some  of  them 
are  even  abundant  in  temperate  climates.  Until  re- 

1  Ituna  and  Thyridia,  Kosmos,  May  1879,  p.  100,  translated  by 
Meldola,  Proc.  Ent.  Soc.  Lond.  1879,  p.  xx. 

2  Nature,  vol.  xxvi.  p.  86. 

*  Ibid.,  vol.  xxix.  p.  405. 

*  Ann.  and  Mag.  Nat.  Hist.  December  1882. 


194         THE  COLOUES  OF  ANIMALS 

cently,  the  British  butterflies  did  not  include  an  ex- 
ample, but  a  large  and  handsome  American  Danaid 
(Danais  archippus)  seems  to  be  gradually  extending 
its  range  into  every  country  where  the  food-pla.nts 
(Asclepiads)  of  its  larva  are  to  be  found.  Several 
individuals  have  been  caught  in  this  country  of  late 


FIG.  48.— The  North  American  Dnnais  arch'ppus,  which  has  now  spread  into 
this  country  ;  upper  side ;  iiiUI  natural  size. 


Pl&.  49. — Danriis  archippus,  showing  the  conspicuous  colours  on  the  under 
sides  of  the  wings. 


years,  and  there  is  no  doubt  that  it  will  thoroughly 
establish  itself  if  it  can  meet  with  a  sufficient  supply 
of  larval  food,  and  can  withstand  the  ceaseless  energy 
of  collectors.  It  is  far  larger  than  any  of  our  native 
butterflies.  It  is  shown  half  the  natural  size  in 
fig.  48,  while  fig.  49  gives  the  appearance  of  the 
under  side.  The  latter  figure  shows  that  the  insect 


WAKNING   COLOUES  195 

must  be  as  conspicuous  at  rest  as  it  is  on  the  wing, 
a  fact  which  is  characteristic  of  those  groups  of 
butterflies  which  are  specially  defended  by  being  un- 
palatable. In  North  America  Danais  archippus  is 
mimicked  by  Limenitis  misippus,  a  butterfly  belonging 
to  a  very  different  group. 

Although  the  general  resemblance  between  the 
species  in  each  of  these  groups  is  doubtless  due  to 
arrested  divergence,  there  is  one  very  interesting 
case  which  is  probably  to  be  explained  by  convergence 
of  groups  which  were  formerly  unlike.  The  Danaids, 
which  are  found  in  the  same  localities  as  the  Heli- 
conias  of  tropical  America,  have  taken  the  peculiar 
appearance  of  the  latter,  in  the  arrangement  of  the 
colours,  and  in  the  long  narrow  form  of  the  wings. 
These  Heliconoid  Danaids  are  therefore  distinguished 
from  all  the  other  members  of  the  group.  It  is  quite 
obvious  that  both  Heliconian  and  Danaids  are  benefited 
by  the  fact  that  the  insect-eating  animals  of  the  region 
they  inhabit  have  to  learn  but  a  single  mode  of  flight, 
shape  of  wing,  and  general  arrangement  of  colours. 

Although  these  resemblances,  produced  by  conver- 
gence or  by  arrested  divergence,  are  transitional  into 
and  often  contain  an  element  of  true  Mimicry,  they 
must  be  distinguished  from  the  latter.  In  true 
Mimicry,  the  mimicking  species  are  without  unplea- 
sant attributes,  and  are  sheltered  under  the  reputation 
of  abundant  and  well-known  forms  in  which  such 
attributes  are  strongly  marked.  In  the  resemblances 


196         THE  COLOUES  OF  ANIMALS 

considered  here,  all  the  similar  forms  possess  unplea- 
sant attributes  although  they  may  possess  them  in 
different  degrees. 

The  remarkable  likeness  between  many  of  the 
species  of  Burnet  Moths  (Zygaenidae)  is  probably  due 
to  arrested  divergence.  They  are  all  conspicuous 
black  and  red  moths,  and  some  of  them  are  known 
to  be  nauseous. 


The  unpleasant  qualities  may  be  concentrated  in  special 
parts,  which  are  so  placed  and  coloured  as  to  attract 
the  attention  of  enemies 

In  certain  cases  the  warning  appearance  is  of  a 
different  kind.  The  organism  possesses  a  highly 
conspicuous  feature  to  which  the  attention  of  an 
enemy  is  directed ;  if  seized,  the  structure  breaks  off 
without  harm  to  the  animal,  but  with  very  unpleasant 
results  to  the  enemy.  It  is  probable  that  this  method 
of  defence  will  be  found  to  be  wide-spread. 


The  defensive  value  of  '  tussocks ' 

Only  recently,  in  the  summer  of  1887,  this  ex- 
planation of  the  beautiful  flat-topped  tufts  of  fine 
hairs,  called  'tussocks,'  which  occur  on  certain  cater- 
pillars, was  shown  to  me  by  the  results  of  an  experi- 
ment.1 The  tufts  are  often  light-coloured,  and  are 

1  Trans.  Ent.  Soc.  Lond.  1888,  pp.  589-91. 


WARNING  COLOURS  197 

generally  placed  on  an  intensely  black  ground  colour, 
which  shows  them  up  and  makes  them  appear  to 
project  more  than  is  actually  the  case.  In  the  well- 
known  '  H'op-dog '  or  '  Tussock '  caterpillar  (Orgyia 
pudibunda)  there  are  four  '  tussocks,'  each  upon  a 
separate  ring,  and  the  furrows  between  these  rings 
are  of  the  most  intense  velvety  black.  They  are  con- 
cealed until  the  caterpillar  is  irritated,  when  the  body 
is  curved  in  a  vertical  direction,  so  that  the  *  tussocks ' 
diverge,  and  the  furrows  appear  as  black  semilunar 
areas  separating  them  and  rendering  them  con- 
spicuous. The  hairs  of  the  '  tussocks '  are  so  fine  and 
so  closely  packed  that  the  tuft  does  not  appear  to  be 
made  up  of  hairs  at  all,  but  to  be  rather  a  fleshy  pro- 
jection from  the  back  of  the  caterpillar,  and  a  most 
convenient  part  for  an  enemy  to  seize.  Fine  as  the 
hairs  are,  they  nevertheless  bristle  with  minute  lateral 
branches,  and  would  certainly  be  most  unpleasant  if 
brought  into  contact  with  the  skin  of  the  mouth.  If 
seized  by  an  enemy,  the  fine  hairs  come  out  in  im- 
mense numbers,  and  produce  such  an  effect  upon 
the  skin  of  the  mouth  that  the  caterpillar  escapes 
unhurt. 

The  following  experiment  suggested  the  explanation 
which  has  just  been  given.  A  caterpillar  of  the 
Common  Vapourer  Moth  (Orgyia  antiqua)  was  intro- 
duced into  a  lizard's  cage,  and  when  attacked,  instantly 
assumed  the  defensive  attitude,  with  the  head  tucked 
in  and  the  '  tussocks '  separated  and  rendered  as 
10 


198  THE  COLOURS  OF  ANIMALS 

prominent  as  possible.  An  unwary  lizard  seized  the 
apparently  convenient  projection ;  most  of  the  '  tus- 
sock '  came  out  in  its  mouth,  and  the  caterpillar  was 
not  troubled  further.  The  lizard  spent  a  long  and 
evidently  most  uncomfortable  time  in  trying  to  get  rid 
of  its  mouthful  of  hairs. 

On  another  occasion  a  full-grown  '  Hop-dog '  was 
offered  to  a  hungry  adult  Lacerta  viridis,  but  the 
lizard  knew  the  danger,  and  kept  trying  to  find  some 
part  of  the  body  which  could  be  safely  seized.  The 
caterpillar  remained  motionless  in  the  defensive 
attitude  during  the  whole  attack,  which  lasted  several 
minutes.  In  this  attitude  the  '  tussocks '  were  held 
in  the  most  tempting  manner,  while  all  other  parts  of 
the  body  bristled  with  sharp  stiff  spines.  This  ex- 
perienced lizard  finally  seized  the  back  of  the  larva 
a  long  way  behind  the  '  tussocks,'  evidently  looking 
upon  the  bristles  as  the  lesser  evil.  Although  killed 
the  caterpillar  was  not  swallowed,  and  it  had  only  been 
seized  after  many  attempts  and  the  closest  examina- 
tion. It  is  quite  clear  that  the  hairy  covering  would 
have  saved  it  from  any  except  a  very  hungry  enemy. 

Evidence  that  Insect-eating  Animals  learn  by  experience 

When  we  compare  the  behaviour  of  these  two 
lizards  we  find  strong  evidence  for  the  opinion  that 
insect-eating  animals  learn  by  experience.  I  have, 
however,  come  across  more  direct  and  convincing 


WAENING  COLOUES  199 

proofs  of  this  conclusion.  Thus,  the  chamseleon  which 
has  been  previously  referred  to  had  just  been  imported 
into  this  country  when  I  received  it,  and  it  had  probably 
never  seen  a  common  hive-bee  in  its  life.  I  put  a  living 
bee  in  the  cage,  and  the  lizard  immediately  began  to 
watch  it,  and,  as  soon  as  it  had  settled,  captured  it 
with  a  dexterous  shot  of  its  long  tongue.  As  the 
tongue  was  being  withdrawn  with  the  bee  adhering  to 
the  sticky  pad  at  its  extremity,  the  chamaeleon  was 
stung  and  immediately  showed  signs  of  discomfort, 
throwing  its  head  from  side  to  side,  and  thus  jerking 
the  bee  off.  For  many  months  after  this  I  put 
bees  into  the  cage  at  irregular  intervals;  but  the 
chamseleon's  education  in  this  direction  was  complete, 
the  single  experience  was  sufficient,  and  no  other  bee 
was  touched. 


Similar  highly-coloured  and  specially  defended  features 
occur  in  certain  Marine  Animals 

A  very  similar  example  from  an  entirely  different 
group  of  animals  has  been  recently  brought  forward 
independently  by  Professor  W.  A.  Herdman l  and  Mr. 
Garstang.  These  naturalists  suggest  that  the  brightly- 
coloured  dorsal  papillae  of  Eolids  (Nudibranchiate 
gastropods)  have  the  same  meaning  as  the  '  tussocks ' 
of  Orgyia,  being  far  more  conspicuous  than  the  rest 
of  the  body,  easily  detached,  and  often  reproduced  by 

1  Report  of  British  Association  at  Neivcastle,  1889. 


200  THE  COLOURS  OF  ANIMALS 

growth  in  two  or  three  days.  The  nematocysts  at  the 
tips  of  the  papillae  would  convey  a  lesson  to  the  enemy 
similar  to  that  taught  by  the  fine  hairs  of  the  'tussocks.' 

Mr.  Garstang  has  now  tested  this  suggestion  by 
experiment,  and  he  finds  that  fish  will  not  attack  the 
Eolids  under  normal  conditions.  He  therefore  threw 
one  of  them  (the  orange  variety  of  Cavolina  Farrani) 
into  the  tank  containing  young  pollack  (Gadus  polla- 
chius),  which  generally  swallow  any  object  while  it  is 
descending  to  the  bottom.  The  Eolid  was  swallowed 
and  rejected  after  a  second  or  two  by  two  fish,  which 
then  shook  their  heads  as  if  experiencing  discomfort. 
Similar  movements  were  made  when  the  fish  were 
induced  to  seize  the  specially  defended  tentacles  of  sea- 
anemones,  and  when  they  attempted  to  swallow  the 
Poly  cirrus,  described  on  p.  201.  Mr.  Garstang  then 
found  that  the  Eolid  causes  a  distinct,  though  faint, 
tingling  sensation  when  placed  on  the  tongue ;  while 
larger  species  (Facelina  coronata  and  Eolis  Alderi) 
produce  much  more  marked  effects. 

The  protectively  coloured  Opisthobranch,  Hermeea 
(see  p.  70),  has  well-developed  defensive  papillae, 
and  Mr.  Garstang  finds  that  whenever  a  shadow 
passes  over  it,  the  head  is  at  once  retracted,  and  the 
papillae  rendered  very  prominent.  This  behaviour  is 
exactly  similar  to  that  described  in  the  larvae  of  Orgyia 
(see  pp.  197-98).  The  reaction  under  the  stimulus 
of  light  is  associated  with  the  unusually  large  eyes  of 
the  genus. 


WARNING  COLOURS  201 

Mr.  Garstang  has  still  more  recently  come  across 
an  instance  of  the  same  kind  in  a  bright  red  marine 
worm,  one  of  the  Terebellidce  (Poly cirrus  aurantiacus), 
which,  unlike  the  rest  of  its  family,  has  dispensed 
with  the  protection  of  a  tube,  and  creeps  about  in  the 
crevices  of  stones  and  among  the  roots  of  Laminaria. 
It  has  an  immense  number  of  long,  slender-  tentacles, 
and  when  touched,  coils  itself  up  in  the  middle  of  them. 
The  tentacles  break  off  very  easily,  and  evidently  possess 
some  unpleasant  attribute.  When  the  animal  is  irri- 
tated the  tentacles  become  brilliantly  phosphorescent, 
so  that  they  are  conspicuous  by  night  as  well  as  day. 
Mr.  Garstang  obtained  experimental  evidence  of  the 
validity  of  this  interpretation.  He  placed  a  specimen  in 
one  of  the  fish-tanks  in  the  Plymouth  Laboratory :  only 
one  pollack  ventured  to  seize  the  worm,  but  ejected  it 
immediately,  and  would  not  touch  it  again.  Another 
fish  made  three  vigorous  attempts  to  swallow  it,  but 
finally  left  it.  Another,  a  very  voracious  rock-fish,  ac- 
tually swallowed  it,  but  immediately  afterwards  began 
to  work  its  jaws  about  as  if  experiencing  discomfort. 
Mr.  Garstang  then  cut  the  head  and  tentacles  away  from 
the  body  and  threw  both  pieces  into  the  pollack  tank : 
the  tentacles  were  untouched,  but  a  fight  took  place 
over  the  body,  which  was  torn  into  several  pieces  and 
swallowed  with  great  relish.  Mr.  Garstang  has  kindly 
allowed  me  to  describe  these  interesting  experiments, 
which  have  only  just  been  made,  and  have  not,  as 
yet,  been  published  elsewhere. 


202         THE  COLOUKS  OF  ANIMALS 


Adventitious  warning  colours 

Under  this  head  we  may  include  a  few  very  in- 
teresting cases  in  which  palatable  animals  make  use 
of  others  which  are  specially  defended  and  conspicuous 
in  order  to  gain  protection.  Such  a  method  of  defence 
bears  the  same  relation  to  Warning  Colours  as  the 
examples  of  Adventitious  Protection  and  Colouring 
bear  to  true  Protective  Eesemblance  (see  pp.  76-80). 

A  mollusc  which  encourages  a  dense  growth  of 
algae  upon  its  shell  is  defended  by  Adventitious  Pro- 
tective Eesemblance ;  if,  however,  the  algae  were 
brilliantly  coloured  and  nauseous  or  poisonous,  the 
example  would  fall  under  Adventitious  Warning 
Colouration. 

Professor  Eomanes l  brings  forward  examples  of  a 
most  interesting  association  of  crabs  with  sea- 
anemones.  He  quotes  from  Mobius 2  the  remarkable 
case  of  *  two  crabs  belonging  to  different  genera  which 
have  the  habit  of  firmly  grasping  a  sea-anemone  in 
each  claw,  and  carrying  them  about ; '  also  from  P.  H. 
Gosse 3  the  fact  that  when  the  sea-anemone  (Adamsia 
palliata)  is  removed  from  its  position  upon  the  shell 
of  the  hermit  crab  (Pagurus  Prideauxii),  which  in- 
variably carries  it,  the  crab  'always  took  it  up  in 


1  Animal  Intelligence,  International  Science  Series,  pp.  233-34. 

*  Beitrage  zur  Meeresfauna  der  Insel  Mauritius. 

•  Zoologist,  June  1859,  pp.  6580-6584. 


WARNING   COLOURS  203 

its  ckws  and  held  it  against  the  shell  "  for  the  space 
of  ten  minutes  at  a  time,  until  fairly  attached  by  a 
good  strong  base."  '  This  fact  seems  to  indicate  that 
the  crab  detaches  and  refixes  its  anemone  when  it 
changes  its  shell  in  the  course  of  growth.  Eomanes, 
however,  quotes  from  Dr.  E.  Ball  *  the  statement  '  that 
when  the  common  Sagartia  parasitica  is  attached  to  a 
stone,  and  a  hermit  crab  is  placed  in  its  vicinity,  the 
anemone  will  leave  the  stone  and  attach  itself  to  the 
hermit's  shell.' 

Mr.  Garstang  tells  me  that  at  Plymouth  there  are 
two  species  of  hermit  crab  associated  with  two  distinct 
species  of  anemone :  the  Pagurussmd  Actinia  mentioned 
on  p.  202,  and  P.  bernhardus,  which  bears  Adamsia 
Rondeletii.  He  finds  that  hermit  crabs  are  eaten  with 
great  relish  by  fish ;  they  are,  in  fact,  much  used  as 
bait  by  fishermen.  Hence  the  association  with  the 
inedible  Actinians  must  be  of  great  service.  When 
the  hermit  crabs  are  young  and  small  they  are  obliged 
to  live  in  shells  without  anemones,  and  Mr.  Garstang 
has  often  found  them,  shells  and  all,  in  the  stomachs 
of  gurnards  and  other  fish.  He  has  never  found  the 
larger  crabs  with  shells  suited  for  Actinians  in  the 
stomachs  of  fish. 

Another  hermit  crab  at  Plymouth  (Pagurus  cua- 
nensis)  is  always  found  in  shells  covered  with  a  bright 
orange-red  sponge  (Suberites  domuncula).  Mr.  Gar- 
stang finds  that  sponges  are  intensely  disliked  by  fish ; 

1  Critic,  March  24,  1860. 


204         THE  COLOUES  OF  ANIMALS 

the  smell  alone  is  generally  sufficient  to  repel  them. 
Many  Crustacea  are  known  to  live  in  the  canal  systems 
of  sponges,  and  are  thus  protected.  The  significance 
of  this  association  is  to  be  found  in  the  fact  that 
Crustacea  are  the  animals  most  relished  and  sought 
after  by  fishes,  and  that  sponges  are  extremely  re- 
pugnant to  the  latter. 

Such  cases  as  these  are  some  indication  of  the 
severity  of  the  struggle  for  existence  among  marine 
forms  of  life.  Very  interesting  evidence  of  this  is  to 
be  found  in  Bateson's  notes  on  the  protective  habits 
of  shrimps  and  prawns.1  He  states  that  the  wrasse 
will  find  a  shrimp  if  the  least  bit  be  exposed,  in  spite 
of  its  protective  colouration.  If,  however,  '  the  sand  be 
fine,  a  shrimp  will  bury  itself  absolutely.'  We  can 
well  understand  the  immense  advantage  which  would 
be  gained  by  a  much  persecuted  crustacean  if  it 
associated  with  some  animal  repugnant  to  its  foes. 

Colours  and  markings  which  direct  the  attention  of  an 
enemy  to  some  non-vital  part,  but  which  are  not 
attended  by  unpleasant  qualities 

From  cases  such  as  those  which  have  been  just 
described  we  pass,  by  a  very  natural  transition,  to 
colours  and  markings  which  attract  the  attention 
of  an  enemy  to  some  non-vital  part  after  the  animal 

1  Journ.  Mar.  Biol.  Ass.,  New  Series,  vol.  i.  no.  2,  Oct.  1889,  pp. 
211  et  seq. 


WARNING   COLOUES  205 

has  been  discovered.  The  part  seized  by  the  enemy 
breaks  away,  and  thus  gives  the  animal  another  chance 
of  escape.  The  cases  differ,  however,  from  the  pre- 
ceding ones  in  that  the  enemy  is  in  no  way  injured 
by  its  mistake.  In  correspondence  with  this  difference 
such  features  are  associated  with  Protective  Kesem- 
blances  leading  to  concealment,  and  are  not  them- 
selves highly  conspicuous,  or  are  only  conspicuous 
when  the  animal  is  thoroughly  on  the  alert.  The 
object  of  these  characters  is  to  direct  attack  to  some 
unimportant  part  after  all  other  methods  of  defence 
have  failed,  after  disguise  has  been  penetrated  or 
speed  surpassed. 

This  is  probably  one  of  the  meanings  of  the 
brightly-coloured  wings  of  butterflies,  in  addition  to 
their  more  obvious  use  in  courtship.  When  the  insect 
is  flying  they  form  a  conspicuous  mark  easily  seized 
by  an  enemy,  and  yet  readily  tearing  without  much 
injury  to  the  insect.  On  this  account  we  generally 
find  the  wings  torn  and  notched  when  an  insect  has 
been  long  on  the  wing. 

In  the  spring  of  1888  I  caught  a  large  number  of 
Clouded  Yellow  Butterflies  (Colias  edusa)  in  Madeira. 
The  limited  number  of  species  in  the  island  (there 
are  only  about  a  dozen),  and  the  abundance  of 
small  omnivorous  lizards  and  of  insect-eating  birds, 
lead  to  the  keenest  pursuit  of  the  butterflies,  and  I 
noticed  that  the  hind  wings  of  a  considerable  pro- 
portion of  the  Clouded  Yellows  were  notched  just 


206         THE  COLOURS  OF  ANIMALS 

behind  the  body.  The  notches  generally  corresponded 
on  both  hind  wings,  the  insect  having  been  seized  at 
the  instant  when  the  wings  came  together  in  flight, 
or  during  one  of  its  short  pauses  upon  a  flower.  From 
the  position  of  the  injury  it  is  clear  that  the  enemies 
were  aware  of  the  situation  of  the  body  and  attempted 
to  seize  it,  but  that  they  had  been  frustrated  by  the 
swift  and  wary  butterfly  with  its  bright  yellow  wings 
extending  behind  the  short  body,  and  offering  an 
apparently  convenient  point  for  seizure.1 

The  bright  yellow  black-bordered  under  wings  of 
the  moths  of  the  genus  Tryphcena  (Yellow  Underwings) 
also  possess  this  among  their  other  meanings,  as  Mr. 
Jenner  Weir  has  pointed  out :  they  are  exposed  during 
flight,  and  their  colours  are  far  brighter  than  any  other 
part  of  the  insect.  It  is  also  very  common  to  find  the 
margin  of  these  wings  notched  in  captured  specimens, 
and  this  is  often  the  case  when  all  other  parts  are  fresh 
and  perfect.  The  red  and  black  under  wings  of  the 
genus  Catocala  (including  the  Bed  and  Crimson 
Underwings)  are  perhaps  useful  in  the  same  way. 

A  still  more  interesting  and  obvious  character  of 
this  kind  is  to  be  found  in  markings  which  actually 
suggest  the  presence  of  a  vital  part,  such  as  an  enemy 
would  be  likely  to  seize.  On  one  occasion  I  intro- 

1  Skertchly  has  found  such  mutilations  not  uncommon  among 
Bornean  butterflies  :  he  also  notices  the  correspondence  of  the  injury 
on  the  two  sides.  The  wings  are  not  torn  in  this  way  by  flying 
through  thick  branches  ;  Skertchly  states  that  even  the  most  fragile 
butterflies  can  pass  unharmed  through  dense  undergrowth. 


WARNING  COLOURS  207 

duced  a  Small  Heath  Butterfly  (Coenonympha  pam- 
philus)  into  a  lizard's  cage.  It  was  at  once  obvious 
that  the  lizard  was  greatly  interested  in  the  large  eye- 
like  mark  on  the  under  side  of  the  fore  wing:  it 
examined  this  mark  intently,  and  several  times  at- 
tempted to  seize  the  butterfly  at  this  spot.  The 
observation  seems  to  point  to,  at  any  rate,  one  use  of 
the  eye-like  markings  which  are  common  on  the 
under  sides  of  the  wings  of  butterflies. 

A  very  perfect  and  elaborate  example  of  the  same 
kind  is  witnessed  in  the  Hair  streak  Butterflies  (Thecla). 
Each  hind  wing  in  these  butterflies  is  furnished  with 
a  '  tail,'  which  in  certain  species  is  long,  thin,  and 
apparently  knobbed  at  the  end.  When  the  butterfly 
is  resting  on  a  flower  the  wings  are  closed  and  the 
hind  wings  are  kept  in  constant  motion,  so  that  the 
'  tails '  continually  pass  and  re-pass  each  other.  This 
movement,  together  with  their  appearance,  causes  the 
'  tails '  to  bear  the  strongest  likeness  to  the  antennae 
of  a  butterfly  ;  the  real  antennae  being  held  so  as  not 
to  attract  attention.  Close  to  the  base  of  the  supposed 
antennae  an  eye-like  mark,  in  the  most  appropriate 
position,  exists  in  many  species.  The  effect  of  the 
marking  and  movement  is  to  produce  the  deceptive 
appearance  of  a  head  at  the  wrong  end  of  the  body. 
The  body  is  short  and  does  not  extend  as  far  as  the 
supposed  head,  so  that  the  insect  is  uninjured  when 
it  is  seized. 

This  interesting  fact  of  the  resemblance  of  the 


208         THE  COLOUKS  OF  ANIMALS 

tails  and  adjacent  parts  to  a  head  in  Thecla  has  been 
long  known :  it  was  first  observed  by  Dr.  Arnold  in 
the  case  of  a  foreign  species  (Thecla  larbas),  and  was 
confirmed  by  Dr.  Forsstrona  in  other  species.  The 
fact  is  quoted  by  Kirby  and  Spence  under  '  Means  of 
Defence  of  Insects,' but  the  interpretation  offered,  that 
the  insects  '  perhaps  thus  perplex  or  alarm  their 
assailants,'  hardly  expresses  the  true  significance  of 
the  character.1 

The  same  fact  was  independently  discovered  by 
Mr.  E.  C.  L.  Perkins  in  1888,  and  this  keen  naturalist 
at  once  perceived  the  meaning  of  the  character — to 
divert  the  attention  of  an  enemy  towards  a  non-vital 
part.  The  discovery  is  of  especial  interest  because  it 
was  made  upon  an  English  species  (Thecla  W-album), 
and  because  Mr.  Perkins  tested  his  explanation  by 
finding  that  this  part  had  been  torn  in  a  considerable 
proportion  of  the  butterflies. 

The  observation  renders  it  extremely  probable 
that  the  slender  '  tails '  which  occur  in  the  same 
position  in  many  '  Blues '  (Polyommatus),  and  the 
bright  colours  and  eye-like  spots  which  are  often 
associated  with  them,  have  a  similar  meaning.  The 
'Blues,'  when  resting  on  a  flower,  have  the  same 
habit  of  moving  the  hind  wings,  as  I  have  often  ob- 
served in  our  common  English  species  which  are 
without  '  tails.'  The  movement  is  such  as  would 
render  the  '  tails '  prominent  and  antenna-like  if 

1  Kirby  and  Spence,  People's  Edition,  1867,  p.  423. 


WARNING   COLOURS  209 

they  were  present ;  and  it  may,  therefore,  have  per- 
sisted from  a  time  when  the  butterflies  possessed  these 
appendages.  . 

Similar  features  in  Reptiles 

A  similar  interpretation  applies  to  the  tails  of 
lizards,  which  break  off  the  instant  an  attempt  is 
made  to  capture  the  animal  by  seizing  this  part.  The 
tail  is,  of  course,  the  first  part  which  the  pursuer  has 
the  chance  of  seizing.  The  great  length  of  the  tail, 
and  the  rapidity  with  which  it  is  renewed  after  being 
shed,  also  support  this  interpretation. 

Similar  features  in  Mammals 

It  is  very  possible  that  the  well-known  peculiarity 
of  the  tail  of  the  dormouse  is  to  be  explained  in  the 
same  manner.  The  large  bushy  tail  of  the  squirrel 
may  possess  a  similar  meaning  (among  others),  for  an 
enemy  in  pursuit  would  be  liable  to  get  only  a  mouthful 
of  fur.  In  the  north  of  Europe  the  squirrels  which 
frequent  the  birches  are  black,  while  those  on  the 
pines  are  brown  :  both  varieties,  which  are  probably 
protective,  become  greyish  in  winter,  and  thus  har- 
monise with  the  frosted  bark.  But  the  tails  of  both 
retain  their  summer  colour,  and  would  be  thus  more 
conspicuous.  This  fact  was  pointed  out  to  me  by  my 
friend  Mr.  H.  Balfour.1 

1  On  the  other  hand  a  seasonal  change  in  the  colour  of  the  tail 


210         THE  COLOUBS  OF  ANIMALS 


Similar  features  in  Mollusca 

Semper  '  has  shown  that  certain  freely  exposed 
and  active  snails  in  the  Philippines  (Helicarion)  have 
the  same  power  of  readily  parting  with  their  tails, 
and  this  is  also  true  of  a  snail  in  the  West  Indies 
(Stenopus).  The  tail,  or  rather  hinder  part  of  the  foot, 
which  the  animal  sheds  when  it  is  seized  and  after- 
wards renews,  is  more  conspicuous  than  the  rest  of  the 
body.  Semper  found  that  the  tails  had  been  shed  in 
about  ten  per  cent,  of  the  individuals  of  a  species 
(Helicarion  gutta)  very  common  in  the  north-east  of 
Luzon. 

Recognition  Markings 

A  special  kind  of  marking  is  often  of  great  value 
in  attracting  the  attention  of  individuals  of  the  same 
species,  instead  of  attracting  the  attention  of  enemies. 
From  its  obvious  relation  to  the  latter  form  of  marking 
it  is  best  included  under  the  division  of  Warning 
Colours.  Mr.  A.  E.  Wallace  has  directed  attention 
to  the  importance  of  Eecognition  Markings,  and  an 
account  of  them  will  be  found  in  his  recently  published 

seems  to  be  not  uncommon  in  certain  localities  in  this  country.  The 
tail  becomes  cream-coloured  at  the  end  of  summer,  but  resumes  its 
ordinary  appearance  at  the  beginning  of  winter.  Smaller  differences 
appear  to  be  general,  the  summer  fur  on  the  tail  being  coarser  and 
more  uniformly  red  than  the  winter  fur.  —Bell's  British  Quadrupeds, 
2nd  edition,  p.  279. 

1  Semper :  Animal  Life,  International  Scientific  Series,  pp.  395 


WARNING   COLOURS  211 

volume, '  Darwinism  '  (pp.  217-27) -1  Such  characters 
may  be  of  use  in  aiding  a  species  to  escape  from  its 
enemies.  Thus  gregarious  mammals, '  while  they  keep 
together,  are  generally  safe  from  attack,  but  a  solitary 
straggler  becomes  an  easy  prey  to  the  enemy ;  it  is 
therefore  of  the  highest  importance  that  in  such  a 
case  the  wanderer  should  have  every  facility  for  dis- 
covering its  companions  with  certainty  at  any  distance 
within  the  range  of  vision '  (loc.  cit.  p.  217).  Kecog- 
nition  Markings  would  be  especially  useful  *  at  a  dis- 
tance or  during  rapid  motion  in  the  dusk  of  twilight, 
or  in  partial  cover.' 

Recognition  Markings  in  Mammals 

A  very  beautiful  and  familiar  illustration  is  given 
by  Mr.  Wallace — the  white  upturned  tail  of  the  rabbit, 
by  which  the  young  and  inexperienced,  or  the  least 
wary  individuals,  are  shown  the  way  to  the  burrow  by 
those  in  front.  It  is  very  interesting  to  compare  this 
marking  with  that  of  the  skunk,  which  has  been  al- 
ready described  as  possessing  a  very  conspicuous  white 
tail.  In  the  latter  case  the  tail  is  held  so  that  the 
slow-moving  animal  is  always  conspicuous,  and  appeals 
to  the  imagination  and  memory  of  its  enemies ;  the 
tail  of  the  rabbit  only  becomes  conspicuous  when  it  is 
needed  by  other  individuals  of  the  same  species,  and 

1  The  principle  of  Recognition  Markings  is  set  forth  in  a  work  by 
the  late  Alfred  Tylor,  Colouration  in  Animals  and  Plants,  1886, 
p.  30. 


212  THE  COLOURS  OF  ANIMALS 

when  the  animal  is  already  alarmed  and  in  full  retreat 
for  a  place  of  security. 

In  this  way  Mr.  Wallace  explains  the  conspicuous 
markings  often  present  on  gregarious  ruminants, 
which  are  nevertheless  protectively  coloured  in  other 
respects.  The  remarkable  differences  in  the  length 
and  form  of  the  horns  of  different  species  are  explained 
in  a  similar  manner. 


Recognition  Markings  in  Birds 

Mr.  Wallace  also  shows  that  such  characters  are 
especially  numerous  and  suggestive  among  birds. 
'  Recognition  Marks  during  flight  are  very  important 
for  all  birds  which  congregate  in  flocks  or  which 
migrate  together ;  and  it  is  essential  that,  while  being 
as  conspicuous  as  possible,  the  marks  shall  not  inter- 
fere with  the  general  protective  tints  of  the  species 
when  at  rest.  Hence  they  usually  consist  of  well- 
contrasted  markings  on  the  wings  and  tail,  which  are 
concealed  during  repose,  but  become  fully  visible 
when  the  bird  takes  flight '  (loc.  cit.  p.  222). 

Recognition  of  Birds'  eggs  may  be  aided  by  variation 
in  certain  species 

It  is  very  probable  that  the  great  variation  in  the 
colours  and  markings  of  birds'  eggs,  which  are  laid 
close  together  in  immense  numbers,  may  possess  this 


WABNING  COLOURS  213 

significance,  enabling  each  bird  to  know  its  own  eggs. 
I  owe  this  suggestive  interpretation  to  my  friend 
Mr.  Francis  Gotch  :  it  is  greatly  to  be  hoped  that 
experimental  confirmation  may  be  forthcoming.  The 
suggestion  could  be  easily  tested  by  altering  the 
positions  of  the  eggs  and  modifying  their  appearance 
by  painting.  Mr.  Gotch's  hypothesis  was  framed 
after  seeing  a  large  number  of  the  eggs  of  the  guillemot 
in  their  natural  surroundings.  It  appears  to  be  a 
more  feasible  explanation  than  that  offered  by  Mr. 
Wallace.  '  The  wonderful  range  of  colour  and  marking 
in  the  eggs  of  the  guillemot  may  be  imputed  to  the 
inaccessible  rocks  on  which  it  breeds,  giving  it  com- 
plete protection  from  enemies  '  (loc.  cit.  p.  214). 


Recognition  Markings  in  Insects 

Turning  to  insects,  I  do  not  believe  with  Mr. 
Wallace  that  colours  and  markings  generally  are  to 
be  explained  in  this  way,  although  many  instances 
of  undoubted  recognition  characters  will  probably  be 
found  among  them.  In  fact,  a  very  interesting 
example  only  recently  came  before  me. 

It  has  been  already  mentioned  that  Lepidopterous 
larvaB  are  especially  subject  to  the  attacks  of  parasitic 
insects  (Hymenoptera  and  Diptera),  which  lay  their 
eggs  in  or  upon  them.  It  is  of  the  highest  importance 
for  a  parasite  to  know  whether  a  larva  is  already 
*  occupied,'  and  also  to  ensure  that  other  parasites 


214         THE  COLOURS  OF  ANIMALS 

shall  recognise  and  avoid  the  larvae  in  which  it  has 
laid  its  eggs.  When  the  eggs  are  laid  within  the  body 
of  a  caterpillar  the  skin  is  pierced,  and  a  small  amount 
of  blood  exudes  and  generally  forms  a  black  clot. 
These  black  spots  are  probably  recognised  by  other 
parasites,  and  the  larva  is  consequently  avoided. 
Although  the  spots  would  disappear  after  a  change  of 
skin,  the  parasites  generally  lay  their  eggs  at  about 
the  same  period  of  larval  growth,  and  would  be 
warned  over  a  considerable  part  of  this  period.  Al- 
though these  are  not,  properly  speaking,  Eecognition 
Markings,  we  shall  see  that  they  form  the  foundation 
on  which  such  characters  have  arisen. 

Other  parasites  (among  the  Hymenoptera),  such  as 
those  of  the  genus  Paniscus,  lay  eggs  upon  the  body  of 
their  prey.  The  eggs  are  pear-shaped,  and  are  firmly 
fixed  by  the  stalk,  which  is  knobbed  at  the  end.  So 
tightly  do  the  eggs  adhere  that  the  caterpillar  can  change 
its  skin  without  removing  them  (see  pp.  275-77). 
Several  eggs  are  fixed  upon  a  large  caterpillar,  two 
or  three  upon  a  small  one,  although  the  number  varies 
greatly  in  different  individuals. 

These  external  eggs  are  black  and  shining,  and 
they  are  very  conspicuous  against  the  colour  of  the 
caterpillar,  which  is  generally  green.  When  Professor 
Weismann  was  staying  with  me  in  the  summer  of 
1887, 1  showed  him  a  larva  of  the  Puss  Moth  (Cerura 
vinuLa)  to  which  several  eggs  were  attached.  This  led 
to  a  discussion  as  to  the  meaning  of  the  colour,  in 


WAKNING  COLOURS  215 

the  course  of  which  we  both  independently  arrived  at 
the  opinion  that  it  is  adapted  to  serve  as  a  warning 
to  other  parasites  that  the  larva  is  already  '  occupied.' 
The  eggs,  being  black,  somewhat  resemble  the  scars 
caused  by  the  introduction  of  internal  eggs,  so  that 
the  species  which  deposit  such  eggs  may  be  warned 
off,  as  well  as  those  of  the  genus  Paniscus. 


216  THE  COLOURS  OF  ANIMALS 


CHAPTEE  XH 

.     PROTECTIVE  MIMICBY 

WE  now  approach  one  of  the  most  interesting  aspects 
of  our  subject,  and  one  that  has  played  an  important 
part  in  the  history  of  evolution  and  of  natural 
selection. 

History  of  the  subject 

The  fact  that  certain  butterflies  belonging  to 
widely  separate  groups,  but  inhabiting  the  same 
localities,  possess  the  most  remarkable  superficial 
resemblance,  has  been  known  for  a  very  long  time. 
An  interesting  quotation  from  Boisduval's  '  Species 
General  des  Lepidopteres  '  (pp.  372,  373)  is  given  by 
Mr.  Eoland  Trimen  at  the  head  of  his  paper  on 
Mimicry  among  African  butterflies.1  Boisduval's  sen- 
tence, written  in  1836,  refers  to  an  African  Swallow-, 
tailed  Butterfly,  which  still  remains  the  most  remark- 
able instance  of  Mimicry  known  in  the  _worldl 
'  C'est  une  chose  bien  remarquable  que  de  voir  la  nature 
creer  a  cote  les  uns  des  autres  1'  Euplcea  Niavius,  le 

1  Linn.  Soc.  Trans,  xxvi.  p.  497. 


PEOTECTIVE  MIMICRY  217 

Diadema  dubia,  et  le  Papilio  Westermanni,  trois 
Lepidopteres  qui  se  ressemblent  presque  completement 
par  le  port,  le  dessin,  et  la  couleur,  quoique  apparte- 
nant  a  des  genres  fort  eloignes  et  de  tribus  differentes.' 

From  1836,  and  the  even  earlier  dates  at  which 
these  remarkable  resemblances  had  been  noticed, 
until  1862,  no  attempt  at  explanation  had  been  made  ; 
but  in  that  year  Mr.  Bates's  classical  paper  appeared.1 
In  this  admirable~essay  the  author  showed  the  advan- 
tage which  must  necessarily  be  gained  by  a  palatable 
form,  hard  pressed  by  enemies,  if  it  sheltered  itself 
under  the  reputation  of  some  conspicuous  species 
well  known  to  be  inedible. 

Only  three  years  before,  Darwin,  writing  to 
Asa  Gray,  had  said :  '  I  cannot  possibly  believe  that  a 
false  theory  would  explain  so  many  classes  of  facts  as 
I  think  it  certainly  does  explain.  On  these  grounds 
I  drop  my  anchor,  and  believe  that  the  difficulties  will 
slowly  disappear.' 2  One  great  difficulty  which  had 
so  long  been  a  puzzle  to  naturalists  was  therefore 
satisfactorily  explained  by  the  new  theory,  within  a 
few  years  of  Darwin's  prediction. 

It  is  most  delightful  to  read  of  the  interest  and 
enthusiasm  with  which  Bates's  paper  was  received  by 
Darwin.  '  In  my  opinion  it  is  one  of  the  most  re- 
markable and  admirable  papers  I  ever  read  in  my 

1  Contributions  to  an  Insect  Fauna   of  the  Amazons  Valley. 
Linn.  Soc.  Trans,  vol.  xxiii. 

2  Life  and  Letters,  vol.  ii.  p.  217. 


218        THE  COLOURS  OF  ANIMALS 

life,'  he  writes.  '  I  am  rejoiced  that  I  passed  over  the 
whole  subject  in  the  "  Origin,"  for  I  should  have  made 
a  precious  mess  of  it.  You  have  most  clearly  stated 
and  solved  a  most  wonderful  problem.  Your  paper 
is  too  good  to  be  largely  appreciated  by  the  mob  of 
naturalists  without  souls ;  but  rely  on  it  that  it  will 
have  lasting  value,  and  I  cordially  congratulate  you 
on  your  first  great  work.'  *  This  was  Darwin's  opinion 
of  a  theory  which  is  often  lightly  criticised  or  even  con- 
demned by  many  biologists  who  offer  nothing  in  its 
place. 

The  relation  of  the  theory  of  Mimicry  to  Evolution 

Mr.  Bates's  paper  afforded  a  twofold  support  to  the 
arguments  in  the  '  Origin  of  Species,'  at  a  very  criti- 
cal time  in  the  history  of  these  opinions.  In  the 
first  place  it  showed  that  an  important  class  of  facts 
was  unintelligible  upon  any  theory  except  that  of 
evolution.  The  proof  of  this  is  best  given  in  Dar- 
win's own  words,  also  quoted  by  Mr.  Francis  Darwin.2 
'By  what  means,  it  may  be  asked,  have  so  many 
butterflies  of  the  Amazonian  region  acquired  then- 
deceptive  dress  ?  Most  naturalists  will  answer  that 
they  were  thus  clothed  from  the  hour  of  their  creation 
— an  answer  which  will  generally  be  so  far  triumph- 
ant that  it  can  be  met  only  by  long-drawn  argu- 
ments ;  but  it  is  made  at  the  expense  of  putting  an 

1  Life  and  Letters,  vol.  ii.  pp.  391-93. 
1  Ibid.,  vol  ii.  pp.  391-92. 


PEOTECTIVE  MIMICEY  219 

effectual  bar  to  all  further  inquiry.  In  this  particular 
case,  moreover,  the  creationist  will  meet  with  special 
difficulties;  for  many  of  the  mimicking  forms  of 
Leptalis  can  be  shown  by  a  graduated  series  to  be 
merely  varieties  of  one  species ;  other  mimickers  are 
undoubtedly  distinct  species,  or  even  distinct  genera. 
So  again,  some  of  the  mimicked  forms  can  be  shown  to 
be  merely  varieties,  but  the  greater  number  must  be 
ranked  as  distinct  species.  Hence  the  creationist  will 
have  to  admit  that  some  of  these  forms  have  become 
imitatory  by  means  of  the  laws  of  variation,  whilst 
others  he  must  look  at  as  separately  created  under 
their  present  guise ;  he  will  further  have  to  admit 
that  some  have  been  created  in  imitation  of  forms 
not  themselves  created  as  we  now  see  them,  but  due 
to  the  laws  of  variation  !  Professor  Agassiz,  indeed, 
would  think  nothing  of  this  difficulty ;  for  he  believes 
that  not  only  each  species  and  each  variety,  but  that 
groups  of  individuals,  though  identically  the  same, 
when  inhabiting  distinct  countries,  have  been  all 
separately  created  in  due  proportional  numbers  to  the 
wants  of  each  land.  Not  many  naturalists  will  be 
content  thus  to  believe  that  varieties  and  individuals 
have  been  turned  out  all  ready  made,  almost  as  a 
manufacturer  turns  out  toys,  according  to  the  tempo- 
rary demand  of  the  market.'  l 

But  Mr.  Bates's  theory  was  equally  important  in 

1  From  a  review  of  Bates's  paper  by  Charles  Darwin. — Natural 
History  Revieiv,  1863,  p.  219. 


220         THE  COLOURS  OF  ANIMALS 

another  respect.  It  not  only  supported  the  doctrine  of 
evolution,  but  it  afforded  strong  confirmation  of  the 
theory  of  natural  selection,  by  which  Darwin  explained 
how  it  was  that  evolution  took  place.  Every  step  in 
the  gradually  increasing  change  of  the  mimicking  in 
the  direction  of  specially  protected  form,  would  have 
been  an  advantage  in  the  struggle  for  existence,  while 
the  elements  out  of  which  the  resemblance  was  built 
exist  in  the  individual  variability  of  the  species,  a 
variability  which  is  hereditary. 


The  transition  from  Warning  to  Mimetic  appearances 

It  will  have  been  observed  that  Mimicry  has  already 
been  mentioned  in  the  pages  on  Warning  Colours,  and 
that  a  gradual  transition  may  be  traced  from  the  one 
principle  to  the  other.  And  yet  Mimicry  itself  was 
explained  long  before  many  of  the  conclusions  con- 
cerning Warning  Colours  which  have  been  described. 
In  this,  as  in  so  many  other  cases,  the  steps  by  which 
the  subject  is  best  approached  are  almost  exactly  oppo- 
site to  the  historical  steps  by  which  it  was  gradually 
understood. 

The  transition  from  warning  to  mimetic  forms 
may  be  shortly  recapitulated. 

1.  The  existence  of  Warning  colours,  attitudes,  &c. 
in  species  which  possess  some  quality  unpleasant  to  the 
enemies  of  their  class  :  recognised  by  Bates  in  butter- 
flies which  are  mimicked  by  others  (loc.  cit.  1862) ;  the 


PROTECTIVE  MIMICRY  9.21 

principle  especially  supported  and  extended  by  Wal- 
lace; also  greatly  supported  by  Trimen,  Belt,  and 
many  others. 

2.  The  tendency  for  the  species  in  each  specially 
protected  group  of  butterflies  to  resemble  each  other 
(by  convergence  or  arrested  divergence)  more  closely 
than  those  in  other  groups  not  similarly  protected, 
thus  suffering  a  smaller  amount  of  destruction  while 
their  enemies  are  being  educated  to  avoid  them  ;  sug- 
gested by  Meldola  ('  Ann.  and  Mag.  Nat.  Hist.'  Dec. 
1882)  as  an  extension  of  the  principle  discovered  by 
Fritz  Miiller  and  described  in  the  next  paragraph. 

3.  The  tendency  for  the  members  of  distantly  re- 
lated groups  of  specially  protected  butterflies  to  resemble 
each   other,  thus  gaining  the   advantages   described 
above  :  discovered  by  Fritz  Miiller   ('  Proc.  Ent.  Soc. 
Lond.'  1879,  p.  xx.).   The  fact  of  the  resemblance  was 
first  observed  by  Bates  (loc.  cit.). 

4.  An  extension  of  the  same  principle  to  all  the 
groups  of  such  specially  protected  animals  :  in  these 
the  same  colours  and  patterns  occur  again  and  again, 
and  advantage  is  gained  by  the  fact  that  the  types  of 
appearance  are  those  which  produce  most  effect  upon 
the  sight  of  an  enemy,  as  well  as  by  the  fact  that  only 
a  few  different  types  have  to  be  learnt.    Certain  types 
of  colour  and  pattern  are  eminently  advantageous  for 
animals  in  which  the  special  protection  is  imperfect, 
because  they  are  so  thoroughly  advertised  by  other 
animals   in   which   the   protection   is   complete   and 

11 


222  THE  COLOURS  OF  ANIMALS 

inspires    great   dread   (Poulton,   « Proc.  Zool.    Soc.' 
March  1887). 

5.  The  latter  cases  naturally  lead  to  those  of 
true  Mimicry,  in  which  a  group  of  animals  in  the 
same  habitat,  characterised  by  a  certain  type  of  colour 
and  pattern,  are  in  part  specially  protected  to  an 
eminent  degree  (the  mimicked),  and  in  part  entirely 
without  the  special  protection  (the  mimickers),  so  that 
the  latter  live  entirely  upon  the  reputation  of  the 
former.  Discovered  by  Bates  in  Tropical  America, 
(loc.  cit.  1862),  then  by  Wallace  in  Tropical  Asia  and 
Malaya  (loc.  cit.  1866),  and  by  Trinien  in  South  Africa 
(loc.  cit.  1870). 


Cases  to  which  the  term  Mimicry  is  best  applied 

The  term  Protective  Mimicry  is  best  applied  to  the 
deceptive  appearance  of  the  unprotected  forms  in  the 
last  class  only.  Instances  of  such  true  Mimicry,  in 
which  the  resemblance  deceptively  suggests  the  pre- 
sence of  some  positively  unpleasant  quality,  are  so 
common  and  striking  that  we  need  some  name  for 
them ;  and  it  is  in  every  way  best  to  retain  the 
historic  term.  An  additional  advantage  is  that  the 
word  Mimicry  implies  the  deception  and  unreality 
which  is  so  obvious  in  the  last  class  of  cases  de- 
scribed above.  For  this  reason  it  is  best  to  include 
all  the  other  classes  and  the  protected  forms  in  the 
fifth  class,  unc|er  Warning  Colours ;  for  their  object 


PROTECTIVE  MIMICRY  223 

is  to  warn  an  enemy,  as  effectually  as  possible,  of 
real  danger  or  unpleasantness  ;  while  the  object  of 
the  unprotected  forms  in  the  fifth  class  is  to  suggest 
the  presence  of  some  unpleasant  attribute  which  has 
no  existence  in  fact. 

The  transition  from  Warning  to  Mimetic  colours 
which  occurs  in  the  fourth  class  is  no  objection  to 
this  arrangement ;  for  we  cannot  escape  transition  in 
any  classification  of  the  uses  of  colour  in  animals. 
Some  authorities  have  failed  to  make  any  distinction 
between  Mimicry  and  the  other  forms  of  Protective  and 
Aggressive  Resemblance ;  but  such  an  arrangement 
would  confound  together  cases  in  which  appearance  is 
used  for  concealment,  and  those  in  which  it  is  made 
use  of  in  order  to  attract  attention.1 


1  S.  B.  J.  Skertchly  has  recently  (Ann.  and  Mag.  Nat.  Hist.,  Series 
vi.  vol.  iii.  pp.  477  et  aeq.)  urged  (a)  that  'protective  resemblance 
copies  stationary  objects,  mimicry  simulates  moving  ones.'  He  accord- 
ingly maintains  that  the  former  is  a  defence  against  enemies  which 
attack  butterflies  at  rest,  the  latter  against  those  which  attack  them 
on  the  wing.  He  further  argues  that  the  attacks  of  birds  constitute 
the  only  real  danger  to  an  insect  on  the  wing ;  (6)  that  certain  ob- 
servers (Skertchly,  Pryer,  Scudder)  agree  in  considering  these  attacks 
to  be  of  very  little  importance ;  and  (c)  that  therefore  Mimicry,  to- 
gether with  the  shyness  of  moving  objects  exhibited  by  all  butterflies 
on  the  wing,  '  are  habits  acquired  long  since,  which  have  survived  the 
necessity  that  gave  them  birth.'  He  maintains  that  this  argument 
is  supported  by  (d)  the  '  law  that  the  amount  of  apprehended  danger 
is  measurable  by  the  efforts  taken  to  avoid  it,'  inasmuch  as  ex- 
amples of  Mimicry  are  far  rarer  than  examples  of  Protective  Resem- 
blance. 

To  this^e  may  reply:  (a)  the  alleged  contrast  between  Pro- 
tective Resemblance  and  Mimicry  is  only  a  usual  consequence  of  the 
real  difference  between  them  (see  pp.  222-23,  also  p.  71).  Further- 


224         THE  COLOURS  OE  ANIMALS 


Convenience  of  the  term  Mimicry 

Mr.  Bates's  term  has  been  criticised  because  it  is 
generally  used  to  describe  voluntary  actions,  whereas 
the  Mimicry  alluded  to  in  these  pages  is  of  course  un- 
conscious, and  has  been  gradually  produced  by  the 
operation  of  natural  selection.1  This  use  of  the  word 

more,  the  alleged  contrast  frequently  breaks  down ;  thus,  a  dead  leaf 
driven  by  the  wind  (see  p.  56),  or  a  piece  of  stick  swinging  by  a  thread, 
are  not  uncommonly  resembled ;  while  the  conspicuous  appearance  of 
Mimetic  and  Warning  Colours  are  most  certainly  of  value  during  rest 
as  well  as  during  flight  (see  pp.  189-95).  Against  the  evidence  offered 
by  Skertchly  (b)  may  be  put  the  observations  of  other  naturalists 
(see  pp.  228-30;  many  other  examples  might  have  been  recorded).  We 
must  also  remember  that  very  little  of  the  destruction  of  life  which 
we  know  takes  place  is  actually  witnessed  by  us.  Against  (c)  may 
be  urged  the  fact  that  characters  begin  to  decline  directly  they  be- 
come useless,  while  certain  mimetic  resemblances  are  perhaps  more 
wonderfully  elaborate  and  perfect  than  anything  else  in  the  animal 
kingdom.  Every  naturalist  will  agree  with  (d),  but  it  is  really  de- 
structive of  the  argument  based  upon  it.  The  danger  to  most 
mimetic  species  must  indeed  be  great  if  measured  by  the  efforts  taken 
to  avoid  it.  Some  of  the  marvellous  results  of  such  '  efforts '  are  de- 
scribed in  this  volume.  Skertchly's  argument  only  applies  to  the 
numerical  ratio  between  the  examples  of  Mimicry  and  Protective 
Resemblance ;  and  this  ratio  is  readily  explicable  on  other  grounds.  It 
has  been  shown  that  Warning  Colours  can  only  be  adopted  safely  by  a 
small  proportion  of  the  insect  fauna  in  any  country  (see  pp.  178-80), 
and  also  that  mimetic  individuals  must  be  far  rarer  than  the  nauseous 
forms  they  resemble  (see  pp.  243-44  ;  see  also  p.  231). 

1  After  this  sentence  had  been  printed  I  came  across  a  most 
extraordinary  statement  of  the  theory  of  Mimicry  by  Skertchly,  I.e. 
This  theory  '  presupposes  (a)  that  danger  is  universal ;  (b)  that  some 
butterflies  escape  danger  by  secreting  a  nauseous  fluid  ;  (c)  that  other 
butterflies  noticed  this  immunity ;  (d)  that  they  copied  it.'  The  opinions 
expressed  in  the  words  I  have  italicised  will  hardly  be  accepted  by  a 


PROTECTIVE  MIMICRY  225 

is,  however,  well  known,  and  is  not  likely  to  mislead 
anyone ;  and  in  addition  to  its  historical  accuracy  the 
word  is  more  convenient  than  any  other,  as  Mr. 
Wallace  has  pointed  out.  Thus  we  obtain  the  con- 
venient series  of  words  —  mimic,  mimicry,  mimetic, 
mimicker,  mimicked,  mimicking. 

Various  degrees  of  affinity  between  mimicking  and 
mimicked  species 

The  various  examples  of  Mimicry  may  be  divided 
according  to  the  affinity  of  the  forms  which  resemble 
each  other.  Thus  a  species  may  mimic  another  closely 
allied  species,  or  one  of  a  widely  separated  family,  of  a 
distinct  order,  class,  or  even  sub-kingdom.  Mr.  Bates 
first  explained  the  Mimicry  of  butterflies  and  moths, 
so  that  in  this  case  the  divergence  between  the  species, 
although  generally  very  great,  is  not  nearly  so  large 
as  that  of  other  examples.  The  former,  however,  in- 
cludes some  of  the  most  striking  examples  known, 
and  will  be  first  described. 

The  Butterflies  which  afford  models  for  Mimicry 

In  giving  some  account  of  Mimicry  among  butter- 
flies, it  is  first  necessary  to  speak  of  the  models  which 
are  most  generally  copied  in  all  the  warmer  parts  of 

single  naturalist.  I  imagine  that  even  the  American  Neo-Lamarckians 
do  not  follow  their  founder  so  far  as  to  believe  that  the  volition  of  an 
animal  could  account  for  all  the  details  of  mimetic  resemblance. 


226         THE  COLOUKS  OF  ANIMALS 

the  world.  These  models  almost  invariably  belong  'to 
the  two  great  families  Danaidce  (including  Euploea, 
Danais,  and  Hestia)  and  Acrceidce,  while  the  Heliconidte 
of  Tropical  America  are  also  mimicked.  It  has  been 
already  pointed  out  that  the  Danaida,  which  inhabit 
the  region  of  which  the  Heliconidce  are  characteristic, 
have  adopted  the  appearance  of  the  latter,  and  may 
therefore  be  called  Heliconoid  Danaidce.1 


Proof  that  the  mimicked  Butterflies  are  specially  pro- 
tected by  a  nauseous  taste  or  smell 

It  is  of  the  greatest  importance  to  prove  that  these 
butterflies  are  specially  protected  in  some  unusual  and 
exceptionally  complete  manner,  so  that  resemblance 
to  them  would  be  advantageous.  All  observers  speak 
of  their  slow  flight,  gaudy  colours,  and  abundance. 
Thus  Mr.  Trimen's  descriptions  of  the  Danaidce  and 
Acrceidce  are  equally  true  of  the  Heliconidce,  and  of  all 
other  butterflies  or  moths  which  are  the  objects  of 
Mimicry.  '  The  slow  flight,  the  conspicuous  colours, 
the  complete  disregard  of  concealment,  no  less  than 
the  great  abundance  of  individuals,  are  characteristics 
indicating  unmistakably  that  these  butterflies  are 
favoured  races,  enjoying  advantages  and  immunities 
above  their  fellows.' 2  The  colours  of  the  under  sides 

1  Bates  called  them  '  Danaoid  Heliconidce,'  but  Trimen  pointed 
out  that  the  transposed  words  more  truly  express  the  relationship 
(loc.  cit.  p.  499). 

2  Loc.  cit.  p.  498. 


PEOTECTIVE  MIMICRY  227 

of  the  wings  are  the  same  as  those  of  the  upper  sides, 
or  at  any  rate  are  equally  conspicuous.  A  peculiar  and 
frequently  unpleasant  smell  has  been  noticed  by  all 
observers  who  have  studied  these  groups.  It  is  pro- 
bable that  the  same  means  of  defence  is  present  in  the 
other  stages,  and  this  has  been  proved  in  certain 
cases  (e.g.  Acraa  horta,  Trimen).  The  unpleasant 
smell  frequently  resides  in  a  clear  yellow  fluid  which 
exudes  on  the  slightest  pressure. 

Mr.  Trimen l  has  also  called  attention  to  the  fact 
that  the  conspicuous  butterflies  and  moths  which 
possess  such  qualities  have  a  remarkably  elastic  struc- 
ture, and  can  endure  very  severe  pressure  without 
injury.  The  wings  are  so  flexible  that  they  can  be 
bent  and  distorted  without  breaking  the  nervures. 
The  insects  can  in  this  way  often  recover  from  the 
mistaken  attacks  of  insect-eating  animals.  Skertchly 
also  maintains,  from  his  experience  in  Borneo,  that 
nauseous  properties  are  accompanied  by  strong 
vitality. 

There  is,  unfortunately,  too  little  direct  experi- 
mental proof  of  the  unpalatability  of  the  specially 
protected  groups  which  are  the  chief  models  of  Mimi  • 
cry.  When,  however,  all  the  observations  are  brought 
together  they  constitute  a  fair  amount  of  evidence, 
and  there  can  be  no  doubt  about  the  results  of  future 
experiments. 

Mr.  Bates   mentions  the   glands  near   the   anus 

1  Loc.  cit.  pp.  498,  499. 


228         THE  COLOUES  OF,  ANIMALS 

of  certain  Heliconid<z,  and  he  noticed  that  they  all 
possess  a  peculiar  smell.  Neither  Bates  nor  Wallace 
saw  them  attacked  by  birds,  dragon-flies,  lizards,  or 
predaceous  flies  (Asilid<z)y  although  all  these  devour 
other  butterflies,  and  the  Heliconida,  from  their  abun- 
dant flocks  and  slow  flight,  would  be  a  particularly 
easy  prey.1 

In  Brazil  and  in  Nicaragua  some  important  obser- 
vations upon  the  Heliconidce  (probably  including  the 
Danaidce)  were  made  by  Mr.  Belt.  He  says :  '  I  have 
seen  even  spiders  drop  them  out  of  their  webs  again  ; 
and  small  monkeys,  which  are  extremely  fond  of 
insects,  will  not  eat  them,  as  I  have  proved  over  and 
over  again.'  *  '  I  observed  a  pair  of  birds  that  were 
bringing  butterflies  and  dragon-flies  to  their  young, 
and  although  the  Heliconii  swarmed  in  the  neighbour- 
hood, and  are  of  weak  flight  so  as  to  be  easily  caught, 
the  birds  never  brought  one  to  their  nest.'  A  tame 
white- faced  monkey  '  would  greedily  munch  up  beetle 
or  butterfly  given  to  him,  and  I  used  to  bring  to  him 
any  insects  that  I  found  imitated  by  others,  to  see 
whether  they  were  distasteful  or  not.  I  found  he 
would  never  eat  the  Heliconii.  He  was  too  polite  not  to 
take  them  when  they  were  offered  to  him,  and  would 
sometimes  smell  them,  but  invariably  rolled  them  up 
in  his  hand  and  dropped  them  quietly  again  after  a 
few  moments.  There  could  be  no  doubt,  however, 

1  Loc.  cit.  p.  510  ;  Darwinism,  p.  234. 
1  Naturalist  in  Nicaragua,  p.  109. 


PROTECTIVE  MIMICRY  229 

from  the  monkey's  actions,  that  they  were  distasteful 
to  him.' 1 

Mr.  Belt,  however,  observed  that  a  yellow  and 
black  wasp  caught  these  butterflies  to  store  up  in  its 
nest,  and  that  the  Heliconida  were  very  wary  when 
the  wasp  was  near,  although  quite  fearless  in  the 
presence  of  other  enemies.  They  were  also  attacked 
by  a  flower-haunting  spider.  These  exceptions  are 
very  interesting,  because  the  unpleasant  qualities  of 
such  specially  defended  groups  generally  appeal  with 
success  to  the  taste  of  animals  from  the  most  widely- 
separated  places  in  the  animal  kingdom.  When  certain 
enemies  are  thus  careless  of  the  qualities  which  inspire 
such  general  respect,  it  is  probable  that  we  witness  a 
result  brought  about  in  the  first  instance  by  the 
excessive  competition  for  food.  In  times  of  scarcity, 
an^  individuals  of  a  species  which  were  able  to 
disregard  the  unpleasant  taste,  would  be  likely  to 
predominate  over  those  with  more  delicate  gustatory 
susceptibilities. 

From  Africa,  Mr.  Trimen  quotes  an  observation  of 
Mr.  Bowker  upon  a  small  Kaffrarian  lizard  which 
pursues  a  peculiarly  wary  butterfly  with  the  greatest 
energy  and  persistence,  while  it  neglects  the  inert  and 
abundant  Acr&idce.  Mr.  Trimen  has  made  similar 
observations  with  regard  to  dragon-flies  and  Mantida, 
both  of  which  feed  largely  on  butterflies,  but  were 
never  seen  to  touch  an  Acrcea  or  Danais.* 

1  Loc.  cit.  pp.  316,  317.  »  Loc.  cit.  p.  500. 


230  THE  COLOUES  OF  ANIMALS 

In  India,  on  the  other  hand,  M.  de  Niceville  found 
that  Acrcea  viola  was  the  only  butterfly  refused  by  all 
the  species  of  Mantis  with  which  he  experimented.  Mr. 
Wallace  quotes  an  observation  by  the  Hon.  Justice 
Newton,  upon  the  bulbul,  which  chases  and  greedily 
devours  a  swift  but  palatable  butterfly,  but  could  only 
be  induced  to  touch  a  Danais  by  repeated  persecution.1 

Some  very  interesting  observations  prove  that  the 
unpleasant  qualities  are  retained  in  the  dried  specimens 
long  after  death.  '  Mr.  Bates  observed  that,  when 
set  out  to  dry,  specimens  of  Heliconidce  were  less 
subject  to  the  attacks  of  vermin ; ' 2  while  Professor 
Meldola  even  found  that  '  in  an  old  collection  which 
had  been  destroyed  by  mites,  the  least  mutilated 
specimens  were  species  of  Danais  and  Euplcea.' 3  This 
observation  has  been  confirmed  by  Mr.  J.  Jenner 
Weir. 

Conclusion  warranted  by  the  evidence 

I  have  brought  together  all  the  available  evidence 
on  this  subject,  because  there  has  been  of  late  years 
a  rather  wide-spread  tendency  to  reject  the  explana- 
tion offered  by  Mr.  Bates.  The  evidence,  however, 
certainly  warrants  the  conviction  that  experiment 
would  prove  all  (protectively)  mimicked  species  to  be  in 
some  way  disagreeable  or  even  dangerous  to  the  enemies 
of  their  class ;  and  if  this  be  so,  the  probability  that 

1  Darwinism,  p.  235.  2  Darwinism,  p.  234. 

»  Proc.  Ent.  Soc.  Land.  1877,  p.  xii. 


PROTECTIVE  MIMICRY  231 

all  mimetic  resemblances  are  due  to  natural  selection 
contrasts  in  the  strongest  manner  with  the  entire 
absence  of  any  alternative  theory  on  the  part  of  Mr. 
Bates's  critics. 


Conditions  under  which  Protective  Mimicry  occurs 

The  conditions  under  which  Mimicry  occurs  also 
strongly  confirm  the  view  that  these  resemblances 
have  been  produced  by  the  operation  of  natural  selec- 
tion. These  conditions  have  been  found  to  be  very 
nearly  constant  by  every  naturalist  who  has  published 
any  observations  on  the  subject.  They  have  recently 
been  very  concisely  stated  by  Mr.  Wallace  as  fol- 
lows.1 

*  1.  That  the  imitative  species  occur  in  the  same 
area  and  occupy  the  same  station  as  the  imitated. 

4  2.  That  the  imitators  are  always  the  more  de- 
fenceless. 

'  3.  That  the  imitators  are  always  less  numerous 
in  individuals. 

5  4.  That  the  imitators  differ  from  the  bulk  of 
then-,  allies. 

4  5.  That  the  imitation,  however  minute,  is  external 
and  visible  only,  never  extending  to  internal  characters 
or  to  such  as  do  not  affect  the  external  appearance.' 

1  Darwinism,  pp.  264.  265. 


232  THE  COLOURS  OF  ANIMAIfl 

Mimicry  in  the  Butterflies  of  Tropical  America 

The  Heliconidce,  and  Danaida  which  resemble  them, 
in  Tropical  America,  are  chiefly  mimicked  by  Pierida 
— the  family  of  '  Whites '  to  which  our  common 
Cabbage  Butterflies  or  Garden  Whites  belong. 
Mr.  Bates  figures  one  non-mimetic  species  of  the 
family,  and  the  resemblance  to  our  familiar  butter- 
flies, together  with  the  immense  difference  between 
it  and  the  mimetic  Pierida  in  the  same  country,  are 
very  striking.  He  also  figures  many  beautiful 
examples  of  Mimicry,  and  the  two  plates  should  be 
studied  by  anyone  who  can  obtain  access  to  Vol.  xxiii. 
of  the  '  Transactions  of  the  Linnean  Society '  (pp. 
495-566).  One  of  the  most  striking  instances  is 
reproduced  in  Mr.  Wallace's  recent  work.1 

Mr.  Bates  found  that  two  different  Heliconidce 
in  two  adjacent  areas  were  in  certain  cases  mimicked 
.by  two  varieties  of  the  same  species  of  Pierid,  a  fact 
which  points  to  the  comparatively  recent  origin  of  the 
resemblance ;  for  otherwise  the  two  varieties  would 
have  had  time  to  become  distinct  species.  A  similar 
fact  was  observed  by  Mr.  Wallace  in  the  Malay 
Archipelago. 

The  specially  protected  forms  were  not  only 
mimicked  by  Pieridce  but  by  Swallow-tails  (Papilio) 
and  other  butterflies,  and  in  many  cases  by  day-flying 
moths  also. 

1  Loc.  tit.  p.  241. 


PROTECTIVE  MIMICRY  233 

I  have  recently  heard  the  objection  raised  to  the 
theory  of  Mimicry,  that  non-mimetic  Pieridce,  with 
the  typical  appearance  of  their  group,  are  among  the 
commonest  butterflies  in  South  America.  It  is  there- 
fore argued  that  the  Pieridce  are  quite  able  to  take 
care  of  themselves,  and,  if  any  of  them  resemble 
other  forms,  it  cannot  be  in  order  to  shelter  them- 
selves under  the  reputation  of  the  latter.  There 
does  not  seem  to  be  much  force  in  this  objection  ;  the 
forces  which  tend  to  the  extermination  of  a  species 
are  so  nicely  balanced  against  the  forces  by  which 
its  existence  is  maintained,  that  a  very  minute  and 
often  quite  inappreciable  difference  may  lead  to  pre- 
dominance or  to  scarcity,  perhaps  ending  in  exter- 
mination. Because  the  typical  Pieridce  in  South 
America  appear  to  be  predominant,  it  by  no  means 
follows  that  all  the  species  of  this  group  have  always 
been  so.  Furthermore,  the  fact  that  all  mimicking 
Pieridce  are  scarce,  and  that  they  invariably  resemble 
the  butterflies  of  specially  protected  groups  which  are 
also  mimicked  by  other  butterflies  and  by  moths,  is 
a  practical  and  complete  answer  to  the  objection. 

Mimicry  in  Asiatic  Butterflies 

In  the  Malayan  islands  and  in  India  Mr.  Wallace1 
found  that  the  Danaidce  are  the  chief  models  for 
Mimicry,  although  certain  Morphidce  and  one  section 

1  Linn.  Soc.  Trans,  vol.  xxv.  pp.  19-22. 


234  THE   COLOURS   OF  ANIMALS 

of  Swallow-tailed  Butterflies  (Papilio)  were  also  re- 
sembled. He  gives  a  list  of  eighteen  examples  of 
mimetic  resemblances  from  among  the  Swallow-tails 
alone.  Among  these  was  an  interesting  case  in  which 
the  males  of  a  Malayan  species  (Papilio  paradoxd) 
mimicked  the  males  of  one  Euplcea  (E.  Midamus), 
while  the  females  mimicked  the  females  of  another 
Euplcea  (E.  Rhadamantlms).  A.  special  section  of 
Swallow-tails  are  also  the  objects  of  Mimicry  in 
South  America. 

The  African  Papilio  merope  as  an  example  of  Mimicry 

By  far  the  most  remarkable  example  of  Mimicry 
is  that  alluded  to  in  the  passage  quoted  from  Bois- 
duval,  and  which  has  been  worked  out,  together  with 
many  other  cases  of  Mimicry,  by  Mr.  Roland  Trimen 
in  South  Africa.  This  wonderful  example  does  not 
appear  to  be  sufficiently  well  known,  although  it  is 
excellently  described  and  illustrated  in  Mr.  Trimen's 
paper,1  from  which  this  account  and  the  figures  upon 
the  coloured  plate  are  taken.  Each  of  the  figures 
has  been  reduced  to  half  the  natural  size. 

2  Fig.  1  closely  resembles  the  male,  while  fig.  2  re- 
presents the  female,  of  a  beautiful  pale  yellow  and 
black  Swallow-tailed"  Butterfly  (Papilio  meriones)  which 
is  found  in  Madagascar.  The  only  marked  difference 
in  colour  between  the  sexes  is  the  larger  amount  of 

1  Linn.  Soc.  Trans,  vol.  xxvi.  pp.  497-522. 

*  See  the  coloured  plate  at  the  beginning  of  the  volume. 


PROTECTIVE  MIMICRY  235 

black  in  the  female.  In  Africa  a  Swallow-tailed 
Butterfly  (Papilio  merope)  occurs,  of  which  the  male 
is  represented  in  fig.  1 ;  the  female,  on  the  other 
hand,  is  without  the  '  tails  '  on  the  hind  wings,  and 
presents  a  totally  different  appearance  from  the  male ; 
it  occurs  in  three  different  varieties,  each  of  which 
mimics  a  different  species  of  Danais  prevalent  in  its 
district. 

Fig.  3  A  represents  Danais  echeria,  a  specially  pro- 
tected butterfly,  common  in  South  Africa,  and  rendered 
conspicuous  by  light  brown  and  white  patches  and  spots 
upon  a  black  ground.  The  appearance  of  the  female 
P.  merope  (the  P.  cenea  form)  in  the  same  locality  is 
shown  in  fig.  3.  It  is  very  interesting  to  find  that 
D.  echeria  is  also  mimicked  by  two  other  species  of 
Swallow-tail  and  by  another  butterfly  (Diadema  mima). 
In  Natal  the  ordinary  form  of  the  Danais  is  replaced 
by  a  variety  in  which  the  spots  on  the  fore  wings  are 
white  instead  of  ochreous.  In  Natal  the  female  P. 
merope  undergoes  a  corresponding  change,  and  inter- 
mDdiate  varieties  of  both  mimic  and  mimicked  are  also 
found. 

The  appearance  of  another  unpalatable  butterfly, 
Danais  niavius,  is  shown  in  fig.  4A.  This  conspicuous 
black  and  white  butterfly  is  abundant  in  tropical 
Western  Africa,  and  it  is  very  faithfully  imitated  by 
two  other  butterflies  in  the  same  locality,  a  Diadema 
and  a  form  of  the  female  of  Papilio  merope  (the  P. 
hippocoon  form),  shown  in  fig.  4.  This  is  the  ex- 


236         THE  COLOURS  OF  ANIMALS 

ample  of  Mimicry  alluded  to  by  Boisduval,  although 
he  uses  different  names  for  the  butterflies.  The 
Natal  form  of  Danais  niavius  is  rather  different, 
having  broader  white  markings,  especially  on  the 
hind  wings,  and  both  its  mimics  have  undergone  a 
corresponding  change  in  the .  same  locality.  The 
Natal  varieties  are  represented  in  figs.  4i  and  4.  It 
is  very  interesting  to  learn  that  the  two  varieties 
of  P.  merope  which  mimic  the  two  species  of  Danais, 
although  so  widely  different  in  appearance,  are  still 
connected  by  intermediate  forms. 

A  third  species  of  Danais,  the  conspicuous  black, 
reddish-brown,  and  white  D.  chrysippus,  is  extremely 
abundant  and  has  a  very  wide  range,  occurring 
throughout  Africa,  in  Southern  Europe,  Southern 
Asia,  the  Malay  Archipelago,  &c.  This  butterfly, 
represented  in  fig.  5A,  is  almost  everywhere  attended 
by  its  mimic,  Diadema  bolina,  which  occurs  in  two 
forms  exactly  resembling  the  two  forms  of  the  Danais. 
A  third  variety  of  the  female  P.  merope  (the  P.  tropho- 
nius  form),  shown  in  fig.  5,  occurs  in  Cape  Colony, 
and  mimics  Danais  chrysippus. 

The  female  of  P.  merope  also  occurs  as  a  fourth 
variety,  unlike  the  others,  but  connected  with  the 
second  of  them  by  an  intermediate  form.  Mr.  Trimen 
considers  that  this  variety  '  is  probably  modified,  or 
in  course  of  modification,  in  mimicry  of  some  other 
protected  butterfly,  possibly  not  a  Danais.' 

To  recapitulate  this  marvellous  instance  of  the 
relations  which  may  obtain  between  the  organisms 


PROTECTIVE  MIMICRY  237 

inhabiting  the  same  land  : — Three  well-known  species 
of  Danais  occur  in  Africa,  each  of  which  is  mimicked 
by  a  special  variety  of  the  female  of  Papilio  merope ; 
two  of  the  Danaidce  present  two  varieties  in  the  range 
over  which  they  are  accompanied  by  the  P.  merope, 
and  some  females  of  the  latter  undergo  corresponding 
changes ;  intermediate  varieties  occur  and  also  connect 
one  of  these  forms  with  a  fourth  variety  of  the  female. 
Furthermore,  in  Madagascar,  which  in  so  many  other 
instances  furnishes  us  with  a  glimpse  of  what  the 
ancestral  African  fauna  must  have  been,  a  Papilio 
is  still  living  with  a  male  like  that  of  P.  merope,  and 
having  a  female  only  differing  in  the  rather  greater 
predominance  of  dark  markings,  a  predominance 
which  is  thus  entirely  in  the  direction  of  the  far  darker 
African  females. 

It  requires  a  very  slight  exercise  of  the  imagina- 
tion to  picture  the  steps  by  which  these  marvellous 
changes  have  been  produced ;  for  here  the  new  forms 
have  arisen  at  so  recent  a  date  that  many  of  the  inter- 
mediate stages  can  still  be  seen,  while  the  parent  form 
has  been  preserved  unchanged  in  a  friendly  land,  where 
the  keener  struggle  of  continental  areas  is  unknown.1 


1  Since  the  appearance  of  Mr.  Trimen's  important  paper,  the 
interest  and  intricacy  of  the  case  have  much  increased.  Mr.  Mansel 
Weale  (Trans.  Ent.  Soc.  Land.  1874,  pp.  131  et  scq.)  found  a  number 
of  the  larva  feeding  together  in  one  locality,  near  King  William's  Town. 
From  these  he  bred  seven  males,  four  females  of  the  Cenea  form,  one 
of  the  Trophonius,  and  one  of  the  Hippocoon  form,  thus  confirming 
Mr.  Trimen's  original  suggestion,  that  all  these  belong  to  the  same 
species.  The  butterflies  have  furthermore  been  taken  in  coitu  more 


238  THE  COLOUKS  OF  ANIMALS 

Protective  Mimicry  more  often  found  in  female 
Butterflies  than  in  males 

This  example  enforces  a  conclusion  arrived  at  by 
the  study  of  mimetic  butterflies  in  all  parts  of  the 

than  once.  Mr.  Mansel  Weale  also  points  out  that  the  sexes  are 
remarkably  different  in  their  manner  of  flight. 

It  is  now  admitted  that  the  West  African  forms  must  be  separated 
from  the  Southern  as  a  distinct  species.  The  western  species  is  now 
called  P.  merope,  while  the  name  P.  cenea  is  extended  to  cover  all 
the  varieties  of  the  southern  species.  The  males  of  the  two  species 
are  very  similar,  but  P.  ccnea  has  somewhat  shorter  wings,  shorter 
tails,  &c.  The  female  P.  cenea  presents  all  three  varieties  described 
above.  The  western  females  lack  the  Cenea  form  which  mimics 
D.  echeria ;  and  the  Hippocoon  form  differs  in  its  larger  size  and 
smaller  extent  of  the  white  markings,  especially  on  the  hind  wing,  in 
these  respects  agreeing  with  the  western  form  of  D.  niavius,  which 
it  mimics.  It  is  interesting  to  note  that  the  western  Trophonius 
form,  mimicking  the  small  D.  chrysippus,  is  little  if  at  all  larger  than 
the  corresponding  form  of  the  southern  species.  A  third  variety  of 
the  western  female,  the  P.  dionysos  form,  is  of  extreme  interest,  in 
that  it  combines  the  features  of  Hippocoon  and  Trophonius,  and  also 
indicates  a  transition  towards  the  female  P.  meriones  of  Madagascar. 
Mr.  Trimen  also  describes  many  varieties  transitional  between  the 
three  forms  of  the  southern  female.  For  further  details  and  a 
thorough  discussion  of  the  whole  question,  consult  Mr.  Roland 
Trimen's  South  African  Butterflies,  vol.  iii.  1889,  pp.  243-55  ;  also 
the  same  author  in  Trans.  Ent.  Soc.  Lond.  1874,  pp.  137  et  seq. 

Two  new  species  have  also  been  added  to  the  P.  merope  group.  In 
the  island  of  Grand  Comoro,  adjacent  to  Madagascar,  another  species, 
P.  Humbloti,  has  been  discovered.  P.  Humbloti  somewhat  resembles 
P.  meriones,  but  the  sexes  are  even  more  alike.  The  other  species, 
P  antinorii,  has  been  found  in  Abyssinia,  and  is  of  extreme  interest, 
in  that  the  sexes  are  nearly  alike,  as  in  the  island  forms.  It  is  much 
to  be  hoped  that  further  research  will  bring  to  light  the  causes  which 
have  favoured  the  persistence  of  the  ancient  unmodified  form  in  this 
one  locality  on  the  mainland  of  Africa. 

I  wish  to  express  my  sincere  thanks  to  Mr.  Roland  Trimen  for 
kindly  looking  through  the  proofs  and  suggesting  references. 


PEOTECTIVE  MIMICRY  239 

world— that  the  females  are  far  more  liable  to 
assume  this  method  of  defence  than  the  males.  Thus 
Mr.  Wallace  found  that  the  eastern  Morphidcs  and 
the  special  group  of  Swallow-tails  were  only  mimicked 
by  the  females  of  other  Swallow-tails  ;  and  similar 
facts  have  been  observed  in  America. 

Mr.  Wallace,  in  his  paper  on  the  Malayan  Swallow- 
tails, explains  the  commoner  mimetic  resemblances  of 
females,  because  '  their  slower  flight,  when  laden  with 
eggs,  and  their  exposure  to  attack  while  in  the  act 
of  depositing  their  eggs  upon  the  leaves,  render  it 
especially  advantageous  for  them  to  have  some  addi- 
tional protection.' 

Mr.  Belt  adopts  the  same  explanation,  and  also 
makes  the  very  ingenious  suggestion  that,  when  the 
males  have  not  been  similarly  modified,  it  is  because 
of  the  preference  of  the  more  conservative  sex  for  con- 
sorts which  retain  the  ancestral  colour  of  the  group 
to  which  they  belong.  He  points  out  that  the  males 
of  many  of  the  mimetic  *  Whites '  (Pierida)  '  have  the 
upper  half  of  the  lower  wing  of  a  pure  white,  whilst 
all  the  rest  of  the  wings  is  barred  and  spotted  with 
black,  red,  and  yellow,  like  the  species  they  mimic. 
The  females  have  not  this  white  patch,  and  the  males 
usually  conceal  it  by  covering  it  with  the  upper  wing, 
so  that  I  cannot  imagine  its  being  of  any  other  use 
to  them  excepting  as  an  attraction  in  courtship,  to 
exhibit  to  the  females,  and  thus  gratify  a  deep-seated 
preference  for  the  normal  colour  of  the  order  to  which ' 


240         THE  COLOURS  OF  ANIMALS 

these  mimetic  forms  belong.1  Ingenious  as  this  sug- 
gestion is,  it  needs  confirmation  by  a  care.ful  observa- 
tion of  the  habits  displayed  during  the  courtship  of 
these  species. 

Protective  Mimicry  in  Moths 

Certain  conspicuous  moths  are  also  mimicked  by 
other  moths  only  distantly  related  to  them.  A  good 
example  was  discovered  at  Amboyna  by  the  naturalists 
of  the  '  Challenger  '  expedition  ;  the  figures  are  repro- 
duced by  Mr.  Wallace.8 

Protective  Mimicry  in  British  Moths  • 

The  only  examples  of  mimicked  species  known 
in  the  British  Lepidoptera  occur  among  the  moths. 
Mr.  Wallace  first  called  attention  to  the  resem- 
blance of  the  female  of  the  Muslin  Moth  (Diaphora 
mendica)  to  the  far  more  abundant  White  Ermine 
Moth  (Spilosoma  menthastri),  both  species  being  white 
with  black  spots,  and  occurring  at  the  same  time  of 
the  year.  The  mimicked  species  has  been  proved  to 
be  unpalatable,  while  the  fact  that  the  male  of  the 
mimicker  is  dark  coloured  and  well-concealed  is  evi- 
dence that  the  latter  is  palatable.  The  conclusion 
should,  however,  be  confirmed  experimentally,  for, 
until  the  test  has  been  applied,  we  cannot  be  sure  that 
the  case  is  one  of  true  Mimicry  rather  than  one  of 

1  Loc.  cit.  pp.  384-85.  2  Darwinism,  p.  247. 


PROTECTIVE  MIMICRY  241 

resemblance  between  unpalatable  forms,  described 
under  Warning  Colours  (see  pp.  191-96).  The  close 
affinity  between  the  two  species,  and  their  similarity 
to  other  closely  related  species,  probably  indicate  that 
the  resemblance  is  due  to  arrested  divergence  rather 
than  convergence ;  if  so,  the  case  before  us  is  not  a 
good  and  typical  example  of  Mimicry. 

A  similar  objection  holds  against  an  example  in 
which  I  have  experimentally  proved  that  the  benefits 
of  true  Protective  Mimicry  are  certainly  conferred.  I 
refer  to  the  unpalatable  and  abundant  white  Satin 
Moth  (Stilpnotia  salicis),  which  is  resembled  by  its 
near  relative,  the  common  white  Gold  Tail  Moth 
(Porthesia  auriflud).  The  abundance  of  the  latter, 
and  the  affinity  between  the  two  species,  make  this 
instance  a  very  bad  one,  but  the  experiments  were  most 
instructive,  and  indicate  the  benefits  derived  from 
Mimicry  in  a  most  suggestive  manner. 


Experimental  evidence  of  the  protection  afforded  by 
mimetic  resemblance 

I  offered  a  Satin  Moth  to  a  marmoset  which  was 
excessively  fond  of  insects,  and  which  had  not  gratified 
this  appetite  for  some  days.  He  seized  the  moth,  and 
ate  it  with  the  strongest  expressions  of  disgust,  well 
known  to  all  who  are  acquainted  with  him ;  in  fact, 
had  not  the  attempt  been  made  to  take  the  moth 
away,  I  believe  that  he  would  have  rejected  it.  As 


242 


THE  COLOURS  OF  ANIMALS 


soon  as  he  had  finished  this  nauseous  morsel,  I  offered 
him  a  Gold  Tail  Moth,  but  he  shrank  from  the  sight  of 
it,  and  had  evidently  had  quite  enough  of  white  moths 
for  the  time  being.  And  yet  he  eagerly  seized  and 
devoured  many  other  inconspicuous  insects  which  I 


FIG.  50.— Satin  Moth  (to  the  left)  and  Gold  Tall  Moth  on  an  ivy  leaf ; 
natural  «ze.  Although  the  moths  are  often  of  the  same  size,  the 
Gold  Tail  is  generally  the  smaller. 


offered  to  him.  It  was  merely  the  resemblance  to  the 
moth  which  had  so  disgusted  him  that  saved  the  Gold 
Tail,  for  on  another  occasion  he  ate  four  of  these 
moths  one  after  the  other  with  the  greatest  relish. 
The  marmoset  has  a  far  more  delicate  taste  than  any 


PKOTECTIVE  MIMICRY  243 

other  insect-eating  animal  with  which!  am  acquainted, 
and  it  appears  therefore  to  be  certain  that  the  Gold 
Tail  Moth  is  palatable.  I  have  also  confirmatory 
evidence  as  to  both  these  species,  from  the  behaviour 
of  other  animals.  The  great  abundance  of  the  Gold 
Tail,  in  spite  of  its  agreeable  taste,  must  be  in  part 
explained  by  the  fact  that  the  caterpillar  is  specially 
protected  in  different  ways  (see  pp.  171-72),  but  it  must 
also  follow  from  the  fact  that  white  and  conspicuous 
moths  are  generally  unpalatable.  The  strong  super- 
ficial resemblance  between  the  two  moths  is  shown  in 
fig.  50. 

Mimicry  may  be  a  source  of  danger  to  the  mimicked 
species 

While  the  experiment  with  the  marmoset  illustrates 
the  benefits  conferred  on  the  mimicker  by  the  well- 
deserved  reputation  of  the  form  it  imitates,  an  experi- 
ment made  by  Professor  Weismann  proves  that  the 
safety  of  both  may  be  endangered  when  the  mimicker 
becomes  relatively  abundant.  Professor  Weismann 
found  that  the  black  and  yellow  caterpillars  of  the 
Cinnabar  Moth  (Euchelia  jacobcece)  were  refused  by 
the  Green  Lizard  (Lacerta  viridis) ;  he  then  introduced 
some  young  caterpillars  of  the  Fox  Moth  (Lasiocampa, 
rubi),  which  are  very  similar  in  appearance.  The 
lizards  first  cautiously  examined  these  larvae,  and  then 


244  THE  COLOURS   OF  ANIMALS 

ate  them.  After  this  they  were  seen  to  taste  the 
Cinnabar  caterpillars,  in  order  to  test  whether  they  were 
really  as  unpalatable  as  they  appeared  to  be.1 


Further  examples  from  the  British  Moths 

Professor  Meldola  has  also  suggested  that  three 
abundant  species  of  Geometrce  (Asthena  candidata, 
Cabera  pusaria,  and  C.  exanthemaria)  may  be  unpalat- 
able, for  they  are  all  white  and  very  conspicuous  when 
flying  at  dusk.  If  this  be-  the  case  it  is  very  probable 
that  the  resemblance  of  two  much  scarcer  Geometers  to 
some  of  these  may  be  an  example  of  true  Mimicry  (viz. 
Acidalia  subsericeata  and  the  first  mentioned  ;  Corycia 
temerata  and  the  second,  or  both  second  and  third). 
It  is  much  to  be  hoped  that  the  experimental  evidence 
will  soon  be  forthcoming. 

I  have  given  many  instances  of  Mimicry  in  Lepi- 
doptera  because  the  subject  has  been  more  fully  in- 
vestigated within  the  limits  of  this  order,  and  because 
of  the  beauty  and  interest  of  the  examples  themselves. 
But  the  same  principles  are  of  very  wide  application, 
as  I  shall  be  able  to  show  in  the  next  chapter,  although 
limited  space  will  prevent  me  from  giving  many  ex- 
amples. 


1  For  these  and  other  experiments  on  unpalatable  insects  see 
Studies  in  the  Theory  of  Descent,  Part  ii.  pp.  336  40 ;  English  trans- 
lation by  Professor  Meldola. 


CHAPTEE  XIII 

PROTECTIVE  AND  AGGRESSIVE  MIMICRY 

WE  have  seen  that  a  Lepidopterous  insect  occasion- 
ally mimics  another  closely  related  to  it,  although  the 
resemblance  is  almost  invariably  between  distantly 
connected  species;  while  in  many  cases  the  relation- 
ship is  very  far  removed,  as  when  a  moth  imitates  the 
appearance  of  a  butterfly.  Corresponding  cases  occur 
in  other  orders  of  insects,  but  we  must  now  pass  on  to 
consider  some  of  the  numerous  instances  in  which  the 
mimetic  species  is  separated  from  the  form  which  it 
deceptively  resembles  by  the  wide  interval  which  re- 
moves one  order  of  insects  from  another. 


Hymenoptera  mimicked  by  other  orders  of  Insects 

The  Hymenoptera,  including  the  formidable  hor- 
nets, wasps,  bees,  and  ants,  are  more  frequently 
mimicked  than  any  other  order.  In  several  of  the 
British  moths  the  wings  have  lost  their  scales  and 
have  become  transparent,  while  the  other  parts  have 

12 


246          THE  COLOUES  OF  ANIMALS 

also  been  modified,  so  as  to  produce  a  more  or  less 
perfect  resemblance  to  some  stinging  Hymenopterous 
insect. 


Eimicry  of  Hymenoptera  by  Lepidoptera 

This  is  the  case  with  two  of  the  hawk-moths,  called 
Bee  Hawks  (Sesia  fuciformis  and  S.  bombyliformis') , 
which  in  some  degree  suggest  the  appearance  of 
humble-bees.  The  habits  are,  however,  entirely  dif- 
ferent, and  the  resemblance  very  imperfect — so  much 
so  that  a  lizard  (Lacerta  muralis),  to  which  I  offered  a 
living  specimen,  was  not  imposed  upon  in  the  least, 
but  devoured  the  insect  without  hesitation  or  caution. 
Although  humble-bees  are  eaten  by  lizards,  they  are 
always  seized  cautiously,  and  disabled  before  being 
swallowed. 

In  one  respect  these  Bee  Hawks  are  extremely  in- 
teresting, for  they  provide  a  conclusive  answer  to  those 
who  believe  that  such  mimetic  forms  have  not  been 
modified  from  a  condition  which  is  more  characteristic 
of  the  group  to  which  they  belong.  When  the  Bee 
Hawk  emerges  from  the  chrysalis  its  wings  are  even 
now  thinly  clothed  with  scales,  which  are  shaken  off 
in  its  first  flight.  The  history  of  the  change  is  still 
recapitulated,  as  in  so  many  other  cases,  in  the  history 
of  the  individual. 

The  two  Hornet  Clear-wing  Moths  (Sphecia  api- 
formis  and  S.  bembeciformis)  afford  far  more  perfect 


PROTECTIVE  AND  AGGRESSIVE  MIMICRY        247 

examples  of  Mimicry,  the  resemblance  to  a  hornet  or 
large  wasp  being  so  strong  that  the  great  majority  of 
people  would  shrink  from  them  in  fear.  The  insect 
carries  out  the  imitation  to  the  end,  and  when  seized 
moves  its  body  as  if  it  were  about  to  sting. 


Experimental  proof  that  Protective  Mimicry  at  first 
deceives  an  enemy 

The  protective  effect  of  the  resemblance  was  well 
seen  when  I  offered  one  of  these  moths  (S.  bembeci- 
formis)  to  Lacerta  muratis.  The  lizard  was  evidently 
highly  suspicious,  and  yet  afraid.  It  examined  the 
insect  very  keenly  from  a  distance,  approached  cau  - 
tiously,  and  touched  it  with  its  tongue.  The  effect  of 
this  investigation  was  evidently  reassuring,  as  we 
might  expect ;  for  the  soft  scaly  body  of  the  moth  is 
very  different  from  the  hard  polished  surface  of  a 
wasp  or  hornet.  And  yet  the  lizard  seized  the  moth 
with  the  greatest  care,  by  the  head  and  thorax,  and 
began  to  thoroughly  crush  these  parts,  behaving  ex- 
actly as  it  would  have  done  with  a  wasp  or  bee.  The 
texture,  and  perhaps  the  taste,  of  the  insect,  however, 
soon  revealed  the  deception,  and  the  lizard  then  treated 
the  moth  as  unscrupulously  as  any  other  harmless 
insect.  A  few  days  afterwards  I  offered  another  moth 
of  the  same  kind  to  the  same  lizard ;  but  the  lesson 
had  been  learnt,  and  the  insect  was  seized  without 


248  THE  COLOUES  OF  ANIMALS 

special  examination  or  caution,  and  devoured  directly 
it  was  seen. 

This  experiment  supports  the  conclusion  previously 
arrived  at,  that  insect-eating  animals  do  not  start 
with  an  instinctive  knowledge,  but  learn  by  experience. 
It  also  proves  that  the  mimetic  resemblance  may 
deceive  a  peculiarly  sharp  and  clever  enemy,  and  cer- 
tainly acts  as  a  protection  to  the  insect.  In  this  case 
the  moth  was  brought  within  a  few  inches  of  the 
lizard :  in  nature  it  would  be  seen  from  a  much  greater 
distance,  and  would,  doubtless,  be  at  once  avoided, 
unless  the  enemy  was  impelled  by  excessive  hunger. 


Mimicry  of  Hymenoptera  by  Diptera 

Other  orders  of  insects  also  commonly  mimic  the 
Hymenoptera.  A  very  common  British  insect  belong- 
ing to  the  Diptera  (the  order  including  flies,  gnats, 
daddy-longlegs,  &c.)  is  known  as  the  Drone-fly 
(Eristalis),  although  it  is  often  wrongly  called  a  Drone. 
It  very  frequently  flies  into  houses,  and  may  be  seen 
walking,  in  a  very  bee-like  manner,  on  the  window- 
panes.  In  addition  to  the  striking  resemblance  to  a  bee 
(see  fig.  51)  it  buzzes  in  a  most  alarming  manner  when 
captured,  and  moves  its  body  in  a  way  that  is  too 
suggestive  for  the  nerves  of  most  people.  And  yet  its 
anatomical  structure  is  entirely  different  from  that  of 
a  bee,  and  a  superficial  examination  will  show  that  it 


PROTECTIVE  AND  AGGRESSIVE  MIMICRY        249 

has  only  two  wings,  instead  of  the  four  possessed  by 
the  Hymenoptera  and  most  of  the  other  orders. 


FIG.  51.— Drone-fly  (EristaZis),  to  the  right,  and  bee  on  a  carrot-blossom  ; 
natural  size. 


Mimicry  of  Hymenoptera  by  Coleoptera 

Among  the  Coleoptera  (beetles)  a  common  English 
beetle  (Clytus  arietis)  resembles  a  wasp  hi  a  very 
striking  manner  (see  fig.  52).  The  slender  waist,  the 
shape  of  the  head  and  antennae,  and  the  black,  yellow- 


250         THE  COLOUES  OF  ANIMALS 

banded  body  are  all  most  suggestive;  and  although 
the  transparent  wings  are  concealed  except  during 
flight,  it  will  be  remembered 
that  the  wings  of  a  wasp 
attract  very  little  attention 
under  the  same  circumstances. 
But  the  most  remarkable 

PIG.  52.— A  common  British  beetle  .     ,     .        .,  ,  , 

(ciytus  arietis)  which  resembles      point  in  the  resemblance  can 

a  wasp ;  natural  size. 

only  be  appreciated  by  observ- 
ing the  living  insect.  When  walking,  the  slender 
wasp-like  legs  are  moved  in  a  rapid  somewhat  jerky 
manner,  very  different  from  the  usual  stolid  Coleo- 
pterous stride,  but  remarkably  like  the  active  move- 
ments of  a  wasp,  which  always  seem  to  imply  the 
perfection  of  training.  Wallace,  Belt,  and  Semper 
also  give  many  instances  of  beetles  and  other  insects 
imitating  the  appearance  of  ants,  which  are  extremely 
abundant,  and  seem  to  be  very  free  from  attack,  in 
the  tropics. 

I  have  chiefly  selected  a  few  common  British  bi- 
sects as  examples  of  Mimicry,  but  the  number  might 
be  multiplied  indefinitely  from  the  insect  fauna  of 
other  countries.  The  examples  are,  of  course,  most 
remarkable  when  the  appearance  of  the  order  to  which 
the  mimetic  form  belongs  diverges  most  widely  from 
that  which  includes  the  imitated  species. 


PROTECTIVE  AND  AGGRESSIVE  MIMICRY         251 


Mimicry  of  Hymenoptera  by  Hemiptera 

The  flattened  bodies  of  the  common  plant-bugs 
(Hemiptera)  are  peculiarly  characteristic,  and  they  are 
in  many  ways  very  unlike  other  insects.  In  spite  of 
the  immense  structural  difference  which  separates 
them  from  the  Hymenoptera,  Mr.  Belt  describes  and 
figures  a  Nicaraguan  bug  which  mimics  a  hornet  so 
closely  that  he  caught  it  in  his  net,  fully  believing 
that  it  was  a  hornet. 

So  common  are  mimetic  resemblances  in  tropical 
countries,  although,  doubtless,  unobserved  by  any 
except  the  keenest  naturalists,  that  Mr.  Belt  writes  : 
'  Whenever  I  found  any  insect  provided  with  special 
means  of  defence  I  looked  for  imitative  forms,  and 
was  never  disappointed  in  finding  them.'  Many  ex- 
amples will  be  found  in  his  most  interesting  book, 
from  which  I  have  already  often  quoted. 

Mimicry  of  Coleoptera  by  Orthoptera 

Many  examples  are  also  given  by  Wallace  l  and 
Semper.2  One  of  the  most  remarkable  is  a  grass- 
hopper (Orthoptera)  from  the  Philippine  Islands, 
which  mimics  a  ladybird,3  and  has  acquired  the 
rounded  convex  shape  which  is  characteristic  of  these 

1  Darwinism,  pp.  257—61. 

*  Animal  Life,  International  Scientific  Series,  pp.  389-91. 

•  Semper,  loc.  cit.  p.  390. 


252  THE  COLOUKS  OF  ANIMALS 

nauseous  little  beetles,  and  is  so  totally  different  from 
the  usual  appearance  of  a  grasshopper.  There  are 
also  many  instances,  from  this  and  other  localities,  of 
insects  resembling  specially  protected  beetles.  Some- 
times the  peculiar  defence  of  the  mimicked  species 
takes  the  form  of  a  hardness  so  extreme  that  insect- 
eating  animals  are  unable  to  make  any  way  against  it. 
Such  uneatable  beetles  are  generally  imitated  by  other, 
and  of  ten  distantly  related,  beetles;  but  there  is  a  cricket 
(Orthoptera)  which  defends  itself  in  this  way.  The 
active  and  predaceous  tiger-beetles  are  also  mimicked 
by  other  beetles  and  insects  of  different  orders.  Thus 
in  the  Philippines  a  harmless  cricket  mimics  one  of 
these  dreaded  insects  in  the  closest  manner. 

A  wonderfully  detailed  example  of  Mimicry  from 
Tropical  America 

One  of  the  most  interesting  cases  I  have  yet  met 
with  was  found  by  my  friend  Mr.  W.  L.  Sclater  in 
Tropical  America.  In  this  part  of  the  world  leaf- 
cutting  ants  are  only  too  well  known,  being  most  de- 
structive of  the  introduced  trees.  They  are  seen  in 
countless  numbers  passing  along  their  well-worn  roads 
to  the  formicarium,  and  every  homeward-bound  ant 
carries  a  piece  of  leaf,  about  the  size  of  a  sixpence,  held 
vertically  in  its  jaws.1  Mr.  Sclater  found  an  insect  of 
an  entirely  different  kind,  and,  I  believe,  belonging  to 

1  An  interesting  account  of  these  ants,  from  which  I  have  taken 
this  short  description,  is  given  by  Mr.  Belt,  Zoc.  cit.  pp.  71  et  seq. 


PROTECTIVE  AND   AGGRESSIVE  MIMICRY        253 

a  different  order,1  which  mimicked  the  ant,  together 
with  its  leafy  burden.  The  piece  of  leaf  was  imitated 
by  a  thin,  flat  expansion,  and  the  resemblance  was  so 
striking  that  Mr.  Sclater's  servant,  who  was  a  keen 
observer,  actually  believed  that  he  was  looking  at  an 
ant  carrying  its  piece  of  leaf. 

Such  cases  can  be  explained  by  the  operation  of 
natural  selection 

This  last  example  is,  as  far  as  I  am  aware,  unique 
in  the  detail  with  which  the  original  is  reproduced ; 
not  only  is  the  specially  protected  species  copied,  but 
it  is  depicted  at  its  usual  occupation,  and  the  material 
upon  which  it  labours  is  also  included  in  the  picture. 
I  quote  below  a  passage  from  Mr.  Belt's  work,  be- 
cause it  expresses  in  the  clearest  and  simplest  way 
what  I  believe  to  be  a  complete  reply  to  those  who 
would  urge  the  incompetence  of  natural  selection  to 
produce  so  faithful  and  detailed  a  likeness. 

'  The  extraordinary  perfection  of  these  mimetic 
resemblances  is  most  wonderful.  I  have  heard  this 
urged  as  a  reason  for  believing  that  they  could  not 
have  been  produced  by  natural  selection,  because  a 
much  less  degree  of  resemblance  would  have  protected 
the  mimetic  species.  To  this  it  may  be  answered  that 
natural  selection  not  only  tends  to  pick  out  and  pre- 
serve the  forms  that  have  Protective  Eesemblances, 

1  Professor  Westwood  and  Mr.  W.  F.  Kirby  believe  that  the  insect 
was  one  of  the  MembracidcB  (Homoptera). 


254  THE  COLOURS  OF  ANIMAIS 

but  to  increase  the  perceptions  of  the  predatory 
species  of  insects  and  birds,  so  that  there  is  a  con- 
tinual progression  towards  a  perfectly  mimetic  form. 
This  progressive  improvement  in  means  of  defence 
and  of  attack  may  be  illustrated  in  this  way.  Suppose 
a  number  of  not  very  swift  hares  and  a  number  of 
slow-running  dogs  were  placed  on  an  island  where 
there  was  plenty  of  food  for  the  hares,  but  none  for 
the  dogs  except  the  hares  they  could  catch ;  the  slowest 
of  the  hares  would  be  first  killed,  the  swifter  preserved. 
Then  the  slowest-running  dogs  would  suffer,  and, 
having  less  food  than  the  fleeter  ones,  would  have  least 
chance  of  living,  and  the  swiftest  dogs  would  be  pre- 
served ;  thus  the  fleetness  of  both  dogs  and  hares  would 
be  gradually  but  surely  perfected  by  natural  selection, 
until  the  greatest  speed  was  reached  that  it  was  possible 
for  them  to  attain.  I  have  in  this  supposed  example 
confined  myself  to  the  question  of  speed  alone,  but,  in 
reality,  other  means  of  pursuit  and  of  escape  would 
come  into  play  and  be  improved.  The  dogs  might 
increase  in  cunning,  or  combine  together  to  work  in 
couples  or  in  packs  by  the  same  selective  process ; 
and  the  hares,  on  their  part,  might  acquire  means  of 
concealment  or  stratagem  to  elude  their  enemies ; 
but,  on  both  sides,  the  improvement  would  be  pro- 
gressive until  the  highest  form  of  excellence  was 
reached.  Viewed  in  this  light,  the  wonderful  perfec- 
tion of  mimetic  forms  is  a  natural  consequence  of  the 
selection  of  the  individuals  that,  on  the  one  side,  were 


PROTECTIVE  AND  AGGRESSIVE   MIMICRY        255 

more  and  more  mimetic,  and,  on  the  other  (that  of 
their  enemies),  more  and  more  able  to  penetrate 
through  the  assumed  disguises.' l  This  argument  is 
of  course  equally  applicable  to  the  wonderful  cases 
of  Protective  Resemblance  for  the  sake  of  conceal- 
ment. 

Insects  mimicked  by  animals  belonging  to  a 
different  class 

We  must  now  pass  on  to  cases  in  which  there  is  a 
still  wider  interval  between  the  mimicker  and  the 
species  which  shelters  it  from  attack.  The  Insecta 
form  one  important  class  of  the  sub-kingdom  Arthro- 
poda,  while  the  Arachnida  (including  the  spiders  and 
scorpions)  constitute  another  of  its  classes.  Very 
important  anatomical  differences  separate  these  two 
classes,  and  yet  members  of  the  latter  are  known  to 
mimic  species  belonging  to  the  former.  Thus,  spiders 
which  mimic  ants  are  known  in  both  the  Old  and  the 
New  World.  One  such  mimetic  spider  was  believed  by 
Mr.  Belt  to  be  an  ant  until  he  had  killed  it.  The 
antennae  of  the  ant  were  represented  by  the  two  fore 
legs  of  the  spider,  and  they  were  held  and  moved 
about  in  the  characteristic  manner.  This  resemblance 
has  been  explained  as  Aggressive  rather  than  Protec- 
tive Mimicry,  enabling  the  spiders  to  approach  the 
ants  upon  which  they  are  supposed  to  prey.  Mr.  Belt, 
however,  points  out  that  the  ants,  being  free  from 

1  Loc.  cit.  pp.  383,  384. 


256  THE   COLOURS  OF  ANIMALS 

attack,  are  very  bold  and  fearless,  so  that  no  disguise 
is  necessary  in  order  to  approach  them.  The  spiders, 
on  the  other  hand,  are  eagerly  sought  for  by  insecti- 
vorous birds;  hence  there  is  little  doubt  that  the 
mimicry  is  protective.1 

E.  G.  Peckham  also  describes  two  ant-like  spiders 
in  North  America.  Synageles  picata  (see  fig.  53)  is 
like  an  ant  in  form  and  colour  ; 
but  '  by  far  the  most  deceptive 
thing  about  it  is  the  way  in 
which  it  moves.  It  does  not 
jump  like  the  other  Attidce,  nor 
does  it  walk  in  a  straight  line, 

PIG.  M.— Synageles  picata  ;  an 

anwjke  spider  (from  Peck-  but  zigzags  continually  from  side 
to  side,  exactly  like  an  ant  which 
is  out  in  search  of  booty.  .  .  .  The  ant  only  moves 
in  this  way  when  it  is  hunting,  at  other  times  it  goes 
in  a  straight  line ;  but  its  little  imitator  zigzags  always.' 
Unlike  Mr.  Belt's  spider,  S.  picata  holds  up  its  second 
pair  of  legs  to  represent  antennae.  «  Spiders  commonly 
remain  nearly  motionless  while  they  are  eating ;  picata, 
on  the  other  hand,  acts  like  an  ant  which  is  engaged  in 
pulling  some  treasure-trove  into  pieces  convenient  for 
carrying.  I  have  noticed  a  female  picata  which,  after 
getting  possession  of  a  gnat,  kept  beating  it  with  her 
front  legs  as  she  ate,  pulling  it  about  in  different 
directions,  and  all  the  time  twitching  her  ant-like 
abdomen.'  This  spider  certainly  does  not  molest  the 

1  Loc.  cit.  pp.  314,  315. 


PROTECTIVE  AND  AGGRESSIVE  MIMICRY        257 

ants  it  resembles,  so  that  the  Mimicry  is  probably  pro- 
tective.  Synemosyna formica  (see  fig.  54)  is  even  more 


Pro.  54.— Synemosyna  formica,  an  ant-like  spider  (from  Peckham). 

like  an  ant  than  S.  picata ;  it  also  holds  up  its  second 
pair  of  legs  as  antennae,  and  its  walk  is  described  as 
very  different  from  that  of  closely  allied  spiders.1 


Insects  which  mimic  Vertebrate  animals 

We  finally  reach  the  most  remarkable  cases  of  Pro- 
tective Mimicry,  in  which  the  defenceless  form  lives 
upon  the  reputation  of  some  dangerous  animal  belong- 
ing to  another  sub-kingdom. 

Mr.  Bates  describes  a  South  American  caterpillar 
which  startled  him,  and  everyone  to  whom  he  showed 
it,  by  its  strong  resemblance  to  a  snake,  and  it  even 
possessed  the  features  which  are  characteristic  of  a 
poisonous  serpent.2 

1  Loc.  tit.  pp.  110-12.  2  Loc.  dt.  p.  509. 


258  THE  COLOURS  OF  ANIMALS 

Equally  interesting  examples  are  to  be  found 
among  our  British  caterpillars.  The  brown  (or  occa- 
sionally green)  mature  larva  of  the  Large  Elephant 
Hawk  Moth  (Chcerocampa  elpenor)  generally  hides 
among  the  dead  brown  leaves  on  the  older  parts  of 
the  stem  of  its  food-plant,  the  Great  Willow-herb 
(Epilobium  hirsutum).  In  this  position  it  is  difficult 
to  see,  for  it  harmonises  well  with  the  colour  of  its 


PIG.  55.— The  caterpillar  of  the  Large  Elephant  Hawk  Moth  (Chcerocampa 
elpenor)  when  undisturbed ;  full-fed  ;  natural  size  (from  Weismann). 

surroundings.  It  possesses  an  eye  like  mark  on  each 
side  of  two  of  the  body-rings  (the  first  and  second 
abdominal  segments);  but  these  markings  do  not 
attract  special  attention  when  the  animal  is  undis- 
turbed. The  appearance  of  the  caterpillar  is  shown 
in  fig.  55. 

As  soon,  however,  as  the  leaves  are  rustled  by  an 
approaching  enemy,  the  caterpillar  swiftly  draws  its 
head  and  the  three  first  body-rings  into  the  two  next 
rings,  bearing  the  eye-like  marks.  These  two  rings 
are  thus  swollen,  and  look  like  the  head  of  the  animal, 
upon  which  four  enormous,  terrible-looking  eyes  are 


PROTECTIVE  AND  AGGRESSIVE  MIMICRY        259 

prominent.  The  effect  is  greatly  heightened  by  the 
suddenness  of  the  transformation,  which  endows  an 
innocent-looking  and  inconspicuous  animal  with  a 
terrifying  and  serpent-like  appearance.  I  well  re- 
member the  start  with  which  I  drew  back  my  hand 
as  I  was  going  to  take  the  first  specimen  of  this  cater- 
pillar that  I  had  ever  seen.  The  appearance  of  the 
closely  allied  C.  porcellus  in  the  alarming  attitude  is 
shown  in  fig.  56.  The  posterior  '  eyes '  are  insignifi- 
cant in  this  species. 


FIG.  56.— The  caterpillar  of  the  Small  Elephant  Hawk  Moth  (Chcerocampa  porcellut) 
in  its  terrifying  attitude  after  being  disturbed  (from  Weismann)  ;  stage  iv. ; 
about  twice  natural  size. 


Such  caterpillars  terrify  their  enemies  by  the  sug- 
gestion of  a  cobra-like  serpent;  for  the  head  of  a 
snake  is  not  large,  while  its  eyes  are  small  and  not 
specially  conspicuous.  The  cobra,  however,  inspires 
alarm  by  the  large  eye-like '  spectacles '  upon  the  dilated 
hood,  and  thus  offers  an  appropriate  model  for  the 
swollen  anterior  end  of  the  caterpillar  with  its  terrify- 
ing markings.  It  is  extremely  interesting  that  the 
caterpillar  should  thus  mimic  a  feature  which  is  only 
deceptive  in  the  snake  itself. 


260  THE  COLOURS  OF  ANIMALS 

Experimental  proofs  of  the  protection  afforded  by 
resemblance  to  serpents 

The  success  of  this  method  of  defence  depends 
upon  an  elaborate  system  of  intimidation.  An  obvious 
criticism  suggests  that  this  interpretation  is  too  fanci- 
ful, and  that  the  appearance  must  have  some  other 
meaning.  It  is  therefore  of  the  highest  importance 
to  bring  forward  direct  evidence  proving  that  insect- 
eating  animals  are  actually  terrified  by  such  cater- 
pillars. 

Professor  Weismann  offered  a  Large  Elephant 
caterpillar  to  a  tame  Jay,  which  immediately  killed 
and  devoured  it.  His  fowls  were,  however,  much 
awed  by  the  appearance  of  a  larva,  although  after 
great  deliberation  one  of  them  ventured  to  attack  it, 
when  the  imposition  was  of  course  instantly  revealed, 
and  the  caterpillar  devoured.  He  then  placed  one  in 
the  seed-trough,  and  found  that  the  sparrows  and 
chaffinches  were  effectually  kept  off  by  it.  One  sparrow 
flew  down  obliquely,  so  that  the  caterpillar  was  hidden 
by  the  side  of  the  trough  until  the  bird  was  close  upon 
it ;  the  instant  the  caterpillar  was  seen,  the  bird  clearly 
showed  its  alarm  by  the  sudden  manner  in  which  it 
altered  its  course.1  Lady  Verney  also  found  that  small 
birds  would  not  come  near  a  tray  containing  bread- 
crumbs when  one  of  these  caterpillars  was  placed 
upon  it.2 

1  Loc.  cit.  pp.  330-33.  •  Good  Wards,  1877,  p.  833. 


PKOTECTIVE  AND  AGGRESSIVE  MIMICRY        261 

I  offered  a  mature  larva  of  the  same  kind  to  a 
full-sized  Green  Lizard  (Lacerta  viridis),  and  closely 
watched  the  encounter.  The  lizard  was  evidently 
suspicious,  and  yet  afraid  to  attack  the  caterpillar, 
which  maintained  the  terrifying  attitude  in  the  most 
complete  manner  throughout.  The  lizard  kept  boldly 
advancing  and  then  retreating  in  fright ;  but  at  each 
advance  it  approached  rather  nearer  to  the  caterpillar. 
After  this  had  taken  place  many  times  and  nothing 
had  happened,  the  lizard  grew  bolder  and  ventured 
to  gently  bite  what  appeared  to  be  the  head  of  the 
caterpillar ;  it  then  swiftly  retired,  but  finding  that 
there  was  no  retaliation,  it  again  advanced  and  gave 
a  rather  harder  bite.  After  a  few  bites  had  been  given 
in  this  cautious  manner,  the  lizard  appeared  satisfied 
that  the  whole  thing  was  a  fraud,  and  devoured  the 
caterpillar  in  the  ordinary  manner.  There  could  be 
no  doubt  whatever  that  the  lizard  was  intimidated  at 
first,  and  that  its  alarm  was  due  to  the  appearance  of 
the  caterpillar.  I  had  often  given  the  same  lizard 
equally  large  hawk  moth  caterpillars  of  other  species, 
and  they  were  invariably  attacked  and  devoured  with- 
out any  ceremony.  I  have  never  seen  a  lizard  behave 
with  such  caution  as  on  the  occasion  I  have  just 
described. 

Lizards  have  good  reason  for  such  an  instinctive 
dread,  for  the  appearance  suggests  that  of  one  of  their 
most  terrible  foes.  Mr.  Belt  graphically  describes  the 
pursuit  of  a  lizard  by  a  snake.  'I  was  once  standing 


262         THE  COLOUES  OF  ANIMALS 

near  a  large  tree,  the  trunk  of  which  rose  fully  fifty  feet 
before  it  threw  off  a  branch,  when  a  green  Anolis 
dropped  past  my  face  to  the  ground,  followed  by  a 
long  green  snake  that  had  been  pursuing  it  amongst 
the  foliage  above,  and  had  not  hesitated  to  precipitate 
itself  after  its  prey.  The  lizard  alighted  on  its  feet 
and  hurried  away ;  the  snake  fell  like  a  coiled-up 
watch-spring,  and  opened  out  directly  to  continue 
the  pursuit ;  but,  on  the  spur  of  the  moment,  I  struck 
at  it  with  a  switch  and  prevented  it.  I  regretted 
afterwards  not  having  allowed  the  chase  to  continue, 
and  watched  the  issue,  but  I  doubt  not  that  the  lizard, 
active  as  it  was,  would  have  been  caught  by  the  swift- 
gliding  snake,  as  several  specimens  of  the  latter  that 
I  opened  contained  lizards.' l 

It  is  almost  certain  that  these  terrifying  appear- 
ances in  the  larvae  of  our  temperate  latitudes  first 
arose  in  warmer  countries,  where  the  danger  decep- 
tively suggested  by  the  Mimicry  is  real  and  obvious. 
The  success  which  attends  this  method  of  defence,  in 
countries  where  the  reptilian  fauna  cannot  be  said  to 
constitute  a  source  of  alarm,  is  similarly  due  to  the 
inheritance  of  instincts  which  arose  in  the  tropics, 
and  which  live  on,  as  that  unconquerable  dread  of  any- 
thing snake-like,  which  is  so  commonly  exhibited  by 
the  land  vertebrates,  including  ourselves. 

*  LOG.  cit.  pp.  339,  340. 


PROTECTIVE  AND  AGGRESSIVE  MIMICRY        263 


Similar  mimetic  resemblance  in  tropical  larvae 

Lord  Walsingham  has  shown  me  some  beautiful 
specimens  of  an  Indian  caterpillar  in  which  the  terrify- 
ing '  eyes  '  are  placed  further  back  than  in  the  Elephant 
Hawks ;  in  fact,  so  far  back  that  the  appearance  of  a 
head  cannot  be  produced  by  telescoping  the  front  part 
into  that  which  bears  the  marks.  The  larva,  however, 
achieves  the  same  end  by  doubling  the  front  part  of  its 
body  beneath  the  rest,  the  bend  being  made  at  the  spot 
where  the  eye-like  marks  are  placed,  so  that  the 


FIG.  57.— Indian  larva  (Ophideres)  in  the  terrifying  attitude  ;  full-fed ;  natural  size. 

latter  are  brought  into  an  appropriate  position  at  the 
anterior  end,  while  the  real  head  is  of  course  concealed 
under  the  body  (see  fig.  57).  The  effect  is  not 
equal  to  that  produced  by  Chcerocampa,  but  it  must  be 
very  striking  when  the  larva  is  partially  concealed 
among  the  leaves  of  its  food-plant. 
'  The  larva  of  the  European  Tau  Emperor  (Aglia 


264  THE  COLOURS  OF  ANIMALS 

Tau)  has  an  eye-like  mark  which  it  can  expose  when 
attacked,  but  which  is  otherwise  concealed.  The 
appearance  of  the  larva  in  its  teTrifying  attitude  is 
shown  in  fig.  58. 


Fio.  58.— The  larva  of  Aglia  Tau  in  its  terrifying  attitude -with  the  eye-Uke 
mark  exposed  ;  full-fed ;  natural  size. 

It  is  obvious  that  this  kind  of  intimidation  re- 
quires a  caterpillar  of  a  considerable  size  in  order  to 
carry  it  off ;  and  as  a  matter  of  fact  we  never  find  it 
attempted  by  small  caterpillars.  A  full-grown  Large 
Elephant  Hawk  is  quite  as  thick  as  a  small  snake,  and 
when  partly  hidden  among  leaves  its  length  might  be 
safely  left  to  the  imagination. 


Some  reasons  why  Mimicry  is  so  frequent  and  perfect  in 
Insects 

Although  mimetic  resemblances  are  far  commoner 
and  more  perfect  among  insects  than  any  other  group 
of  animals,  the  phenomena  will  probably  be  found  to 
occur  very  widely  when  attention  is  directed  to  the 
subject.  It  is,  however,  very  unlikely  that  any  one 
group  of  animals  employs  this  method  of  defence  to 
an  extent  which  at  all  approaches  the  insects.  The 
defenceless  character  of  the  group  as  a  whole,  the 


PROTECTIVE  AND   AGGRESSIVE  MIMICRY        265 

extent  to  which  they  are  preyed  upon  by  the  higher 
animals,  their  enormous  fertility,  and  the  rapidity 
with  which  the  generations  succeed  each  other,  are 
reasons  why  natural  selection  operates  more  quickly 
and  more  perfectly  than  in  other  animals,  producing 
mimetic  resemblances  or  other  forms  of  Protective 
Kesemblance  in  number  and  fidelity  of  detail  un- 
equalled throughout  organic  nature. 

Protective  Mimicry  in  Vertebrata 

Mimicry  is  by  no  means  unknown  among  the  Ver- 
tebrate animals.  Thus  the  brightly  coloured  snakes 
of  the  genus  Elaps,  already  alluded  to,  are  closely 
resembled  by  harmless  snakes  belonging  to  different 
families.  The  names  of  several  mimetic  species,  and 
further  instances  of  the  same  kind  among  African 
snakes,  will  be  found  in  Mr.  Wallace's  '  Darwinism.' 
The  same  writer  also  gives  many  instances  of  Mimicry 
in  birds.  Thus  the  powerful  and  aggressive  friar- 
birds  in  the  Malay  Archipelago  are  exactly  mimicked 
by  weak  and  timid  orioles,  representative  species  of 
both  friar-bird  and  oriole  occurring  in  several  of 
the  islands.1 

Two  classes  of  Protective  Mimicry 

Two  classes  may  be  distinguished  among  the  pre- 
ceding examples.  In  the  vast  majority  of  cases  the 

1  Loc.  tit.  pp.  261-64. 


266         THE  COLOURS  OF  ANIMALS 

mimicking  species  is  defended  against  the  enemies 
which  are  afraid  of  or  dislike  the  mimicked  form.  In  a 
relatively  few  cases,  however,  it  seems  to  be  defended 
from  the  attacks  of  the  mimicked  form  itself.  Thus 
Bates  describes  a  genus  of  South  American  crickets 
(Scaphura}  which  closely  resemble  'different  sand 
wasps  of  large  size,  which  are  constantly  on  the  search 
for  crickets  to  provision  their  nests  with.'  Another 
cricket  resembled  a  predaceous  tiger-beetle,  and  was 
'  always  found  on  trees  frequented  by  the  beetles.' 1 
A  few  other  examples  will  be  found  in  the  preceding 
pages. 

Aggressive  Mimicry 

In  most  cases  of  Aggressive  Mimicry  one  species 
resembles  another  in  order  to  be  able  to  approach  it 
without  exciting  suspicion.  The  former  is  thus  able 
to  injure  the  latter  in  some  one  of  the  ways  which 
will  be  described  below.  Aggressive  Mimicry  is  far  less 
common  than  Protective  Mimicry. 

Trimen  has  shown  that  hunting  spiders  are 
sometimes  very  like  the  flies  on  which  they  prey. 
The  general  resemblance  in  size,  form,  and  colouring 
is  greatly  aided  by  the  movements  of  the  spiders,  which 
evidently  mimic  '  the  well-known  movements  so  cha- 
racteristic of  flies.'  Bates  has  described  a  Mantis  which 
closely  resembles  the  white  ants  on  which  it  feeds. 

In  some  cases  the  Mimicry  enables  the  aggressive 

1  Loc.  cit.  p.  509. 


PROTECTIVE   AND   AGGRESSIVE  MIMICRY        267 

form  to  lay  eggs  in  the  nest  of  that  which  it  resembles, 
so  that  its  larvae  live  upon  the  food  stored  up  by  the 
latter  or  even  upon  the  larvae  themselves.  The  bold- 
ness of  these  enemies  sometimes  depends  upon  the 
perfection  of  their  disguise.  Thus  the  larvae  of  flies 
of  the  genus  Volucella  live  upon  the  larvae  of  bees  and 
•wasps.  Volucella  bombylans  occurs  in  two  varieties, 
which  prey  upon  the  humble-bees,  Bombus  muscorum 
and  B.  lapidarius,  and  are  respectively  like  these  Hy- 
menoptera.  The  resemblance  is  very  perfect,  and  the 
flies  enter  the  nests  to  lay  their  eggs.  Volucella  inanis 
is  less  like  the  common  wasp  (Vespa  vulgaris),  and  only 
dares  to  lay  its  eggs  in  the  evening  at  the  entrance  of 
the  nest,  so  that  the  larvae  may  crawl  in,  or  they  or 
the  eggs  may  be  accidentally  carried  in  by  the  wasps.  It 
is  said  that  the  resemblance  often  fails  to  conceal  the 
fly,  which  is  then  killed  by  the  wasps.1  Some  Hyme- 
noptera  also  live  upon  the  labours  of  other  species  of 
the  same  order,  and  often  resemble  the  species  they 
delude.  Thus,  bees  of  the  genus  Psithyrus  closely 
resemble  humble-bees  (Bombi)  :  they  lay  their  eggs 
in  the  nests  of  the  latter,  and  their  larvae  are  developed 
among  those  of  the  Bombi.* 

1  Mr.  C.  R.  L.  Perkins  attributes  the  cautious  habits  and  frequent 
failure  of  V.  inanis  to  the  acuteness  and  ferocity  which  distinguish 
the  wasps  from  humble-bees. 

2  Mr.  Perkins  considers  that  the  Mimicry  is  intended  to  enable  the 
Psithyri  to  leave  the  nests  after  emerging  from  the  pupa,  rather  than 
to  enable  the  mature  females  to  deposit  their  eggs  in  it. 


268         THE  COLOURS  OF  ANIMALS 


The  mimicking  form  may  prey  upon  some  animal  which 
accompanies  the  species  mimicked 

In  certain  cases  the  Aggressive  Mimicry  is  of  a 
different  kind :  the  mimicking  species  preys  upon 
some  animal  which  is  not  afraid  of  the  mimicked 
species,  or  which  even  lives  in  company  with  the 
latter.  Thus  E.  G.  Peckham  thinks  it  possible  that 
the  ant-like  spider,  Synageles  picata  (see  fig.  53,  page 
256),  may  prey  upon  beetles  which  accompany  ants.1 
As  this  does  not  appear  to  be  sufficiently  proved,  I 
have  retained  the  spider  as  an  example  of  Protective 
Mimicry.  Professor  Meldola  has  suggested 2  that  cer- 
tain ant-like  spiders  from  Africa,  described  by  Mansel 
Weale,  are  enabled  to  approach  the  flies  on  which  they 
prey,  because  the  latter  are  not  afraid  of  ants ;  for 
ants  and  flies  may  be  seen  feeding  together  upon  the 
sweet  secretion  of  the  same  tree.  ^ 

The  clear  distinction  of  both  Protective  and  Aggres- 
sive Mimicry  into  two  classes  I  owe  to  E.  G.  Peckham. 3 

1  Loc.  cit.  p.  111. 

*  Proc.  Ent.  Soc.  Lond.  1878,  p.  xix 

•  Loc.  cit.  p.  103. 


ST4TEWORMALSCHOOL, 

LOB  AH0HJDSL  -:-  CAL. 


CHAPTER  XIV 

THE  COMBINATION  OF  MANY  METHODS  OF 
DEFENCE 

IT  has  already  been  shown  by  repeated  examples  that, 
although  the  various  uses  of  colour  are  quite  Distinct 
from  one  another,  they  are  frequently  combined  in  a 
single  animal.  Thus  the  larvae  of  the  Elephant  Hawk 
Moths  (Charocampa  elptnor  and  C.  porcettus)  were 
shown  to  be  well  concealed  among  brown  leaves  ;  but 
they  assume  a  terrifying  attitude  when  detected  and 
attacked.  I  will  now  bring  forward  two  striking  ex- 
amples of  the  different  lines  of  defence  which  are 
successively  adopted  by  certain  caterpillars. 

The  larva  of  Puss  Moth  well  concealed  by  General 
Protective  Resemblance 

The  larva  of  the  Puss  Moth  (Centra  vinuld)  is 
very  common  upon  poplar  and  willow.  The  circular 
dome-like  eggs  are  laid,  either  singly  or  in  little  groups 
of  two  or  three,  upon  the  upper  side  of  the  leaf,  and 
being  of  a  reddish  colour  strongly  suggest  the  appear- 
ance of  little  galls  or  the  results  of  some  other  injury. 
13 


270         THE  COLOUES  OF  ANIMALS 

The  youngest  larvae  are  black,  and  also  rest  upon  the 
upper  surface  of  the  leaf,  resembling  the  dark  patches 
which  are  commonly  seen  in  this  position.  As  the 
larva  grows,  the  apparent  black  patch  would  cover  too 
large  a  space,  #nd  would  lead  to  detection  if  it  still 
occupied  the  whole  surface  of  the  body.  The  latter 
gains  a  green  ground-colour  which  harmonises  with 
the  leaf,  while  the  dark  marking  is  chiefly  confined  to 
the  back.  As  growth  proceeds  the  relative  amount  of 
green  increases,  and  the  dark  mark  is  thus  prevented 
from  attaining  a  size  which  would  render  it  too  con- 


PIG.  59.— The  larva  of  Puss  Moth  (C.  vinul/i)  when  undisturbed; 
full-fed;  natural  size. 

spicuous.  In  the  last  stage  of  growth  the  green  larva 
becomes  very  large,  and  usually  rests  on  the  twigs  of 
its  food-plant  (see  fig.  59).  The  dark  colour  is  still 
present  on  the  back  but  is  softened  to  a  purplish 
tint,  which  tends  to  be  replaced  by  a  combination  of 
white  and  green  in  many  of  the  largest  larvae.  Such 
a  larva  is  well  concealed  by  General  Protective 
Eesemblance,  and  one  may  search  a  long  time  before 
finding  it,  although  assured  of  its  presence  from  the 
stripped  branches  of  the  food-plant  and  the  faeces  on 
the  ground  beneath. 


COMBINATION  OF  MANY  METHODS  OF  DEFENCE      271 


The  same  larva  assumes  a  terrifying  attitude  (mimetic 
of  a  vertebrate  appearance)  when  disturbed 

As  soon  as  a  large  larva  is  discovered  and  disturbed 
it  withdraws  its  head  into  the  first  body-ring,  inflating 
the  margin,  which  is  of  a  bright  red  colour.  There  are 
two  intensely  black  spots  on  this  margin  in  the  appro- 
priate position  for  eyes,  and  the  whole  appearance  is 
that  of  a  large  flat  face 
extending  to  the  outer 
edge  of  the  red  margin 
(see  fig.  60).  The  effect 
"is  an  intensely  exag- 
gerated caricature  of  a 
vertebrate  face,  which  is 
probably  alarming  to  the 
vertebrate  enemies  of  the 
caterpillar.  The  terrify- 
ing effect  is  therefore  mimetic.  The  movements  en- 
tirely depend  on  tactile  impressions  :  when  touched 
ever  so  lightly  a  healthy  larva  immediately  assumes 
the  terrifying  attitude,  and  turns  so  as  to  present  its 
full  face  towards  the  enemy ;  if  touched  on  the  other 
side  or  on  the  back  it  instantly  turns  its  face  in  the 
appropriate  direction. 


FIG.  60.— The  larva  of  Puss  Moth  in  its 
terrif  yingattitude  after  being  disturbed  j 
full-fed ;  natural  size. 


272  THE  COLOURS  OF  ANIMAI3 


Effect  heightened  by  two  pink  whips 

The  effect  is  also  greatly  strengthened  by  two  pink 
whips  which  are  swiftly  protruded  from  the  prongs 
of  the  fork  in  which  the  body  terminates  (see  fig.  61). 
These  prongs  represent  the  kst  pair  of  larval  legs, 
which  have  been  greatly  modified  from  their  ordinary 
shape  and  use.  The  end  of  the  body  is  at  the  same 
time  curved  forward  over  the  back  (generally  much 


FIG.  61. — One  of  the  pink  whips  of  larva  of  Puss  Moth,  completely 
protruded  from  the  conical  receptacle ;  x  4. 

farther  than  in  fig.  60),  so  that  the  pink  filaments  are 
brandished  above  the  head.  Although  the  filaments 
are  no  thicker  than  a  rather  coarse  cotton  thread, 
they  are  hollow,  and  contain  a  delicate  muscle  which 
runs  through  their  whole  length  and  is  attached  at 
the  top.  When  the  muscle  contracts  the  filament  is 
withdrawn,  being  turned  outside  in :  protrusion  is 
brought  about  by  the  pressure  of  the  blood,  which 
drives  the  filament  before  it.  The  process  could 
be  almost  exactly  imitated  by  fastening  a  string  to 
the  tip  of  the  finger  of  a  glove  and  letting  the  string 
pass  down  inside  the  finger  and  out  at  the  wri/.t. 


COMBINATION  OF  MANY  METHODS  OF  DEFENCE      273 

The  finger  could  then  be  withdrawn  by  pulling  the 
string,  and  protruded  by  blowing  into  the  glove.  The 
filaments  are  especially  used  in  young  and  half-grown 
larvae ;  the  larger  caterpillars  often  lose  the  power  of 
protruding  them. 

The  appearance  of  the  caterpillar  is  sufficiently 
alarming  to  human  beings,  and  most  people  believe 
that  the  black  marks  are  really  eyes.  Eosel  was 
afraid  to  touch  the  larva  when  it  assumed  its  terrify- 
ing attitude.  Izaak  Walton  speaks  of  the  black  marks 
as  '  his  eyes  black  as  jet,'  in  a  description  which,  by 
the  way,  is  a  translation  of  the  Latin  account  given 
by  Muffett  (or  Moufet),1  or  more  probably  slightly 
modified  from,  the  account  in  Topsell's  'History  of 
Serpents '  (!)  which  is  borrowed  from  Muffett.8 


The  care  necessary  if  we  are  to  obtain  experimental 
proof  of  the  protective  value  of  such  terrifying 
appearances 

I  have  found  that  the  marmoset  was  certainly 
terrified  by  a  large  Puss  caterpillar,  and  although  it 
is  said  to  be  greedily  devoured  by  birds,  I  do  not 
expect  that  the  experiment  was  carried  out  in  a 
manner  at  all  fair  to  the  larva.  When  a  larva  is  un- 
scrupulously flung  into  a  cage  by  some  one  from 

1  Insectomm  sive  minimorum  Animalium  Theatrum.  London, 
1634,  p.  183. 

'*  London,  1658,  p.  666. 


274         THE  COLOUKS  OF  ANIMALS 

whom  the  birds  expect  to  be  fed,  it  is  almost  certain 
to  be  attacked  before  it  has  a  chance  of  assuming  its 
terrifying  attitude.  In  conducting  such  an  experi- 
ment a  healthy  vigorous  larva  should  be  chosen  and 
carefully  introduced,  so.  that  it  may  have  the  same 
opportunities  of  defence  which  it  would  possess  in 
a  wild  state. 


The  larva  of  Puss  Moth  can  further  defend  itself  by 
ejecting  ao  irritant  fluid 

All  the  defensive  measures  hitherto  described  are 
of  a  passive  nature,  but  if  further  attacked  the  cater- 
pillar can  defend  itself  in  a  very  effective  manner. 
The  lower  part  of  the  red  margin  below  the  real  head 
of  the  animal  is  perforated  by  a  slit-like  opening  (see 
fig.  60),  leading  into  a  gland  which  secretes  a  clear 
fluid.  This  fluid  is  stored  up  in  considerable  quantity 
and  is  ejected  with  great  force  when  the  caterpillar  is 
irritated.  The  '  face '  being  turned  towards  any  point 
at  which  the  larva  is  touched,  the  stream  is  sent  in 
the  direction  of  the  enemy.  It  has  been  long  known 
that  this  fluid  causes  acute  pain  if  it  enters  the  eye. 

In  working  out  the  chemistry  of  this  secretion  I 
have  been  very  kindly  helped  by  many  eminent 
chemists.  My  thanks  are  especially  due  to  Professor 
R.  Meldola  and  Mr.  A.  G.  Vernon  Harcourt.  The 
secretion  proved  to  be  a  mixture  of  formic  acid  and 
water :  in  a  mature  larva  the  proportion  of  acid  is  as 


COMBINATION  OF  MANY  METHODS  OP  DEFENCE      275 

high  as  forty  per  cent.,  and  a  twentieth  of  a  gramme 
can  be  ejected  if  the  caterpillar  has  not  been  irritated 
for  some  days.  Half  grown  individuals  eject  nearly 
as  much,  but  the  fluid  is  weaker,  containing  about 
thirty-three  to  thirty-five  per  cent,  of  acid.  The  rate 
of  secretion  is  slow ;  two  days  and  a  half  after  the  fluid 
had  been  collected  from  two  large  caterpillars  they  only 
yielded  a  fortieth  of  a  gramme  between  them.1  So  far 
as  we  know  at  present,  no  other  animal  secretes  a 
fluid  containing  anything  which  approaches  this  per- 
centage of  strong  acid. 

The  value  of  this  strongly  irritant  liquid  is  suffi- 
ciently obvious.  I  have  seen  a  marmoset  and  a  lizard 
affected  by  it,  and  have  myself  twice  experienced 
sharp  pain  as  the  result  of  receiving  a  very  small 
quantity  in  the  eye.  Although  the  secretion  is  there- 
fore useful  as  a  defence  against  vertebrate  enemies,  it 
is  probably  chiefly  directed  against  ichneumons. 

The  most  deadly  enemy  of  the  larva  of  the  Puss  Moth 

The  caterpillar  of  the  Puss  Moth  is  especially 
attacked  by  an  ichneumon  (Paniscus  cephalotes),  which 
attaches  its  shining  black  eggs  to  the  surface  of  the  skin. 
These  eggs  are  always  fixed  in  such  a  position  behind 
the  head  that  the  caterpillar  cannot  bite  them  or  the 
maggots  which  hatch  from  them,  and  on  a  spot  where 

1  For  further  details  of  this  investigation  see  Report  of  British 
Association  at  Manchester,  1887,  pp.  765-66. 


276  THE  COLOUES  OF  ANIMALS 

the  ichneumon  would  probably  escape  the  shower  of 
formic  acid.  I  have  never  witnessed  the  attack,  but  I 
imagine  that  the  ichneumon  swoops  down  upon  the 
back  of  the  larva  just  behind  the  head,  and  holds  on  so 
tightly  with  its  sharp  claws  that  it  cannot  be  dislodged 
by  the  violent  struggles  of  the  caterpillar.  Probably 
many  fail  and  are  struck  by  the  acid  shower,  which 
has  a  very  fatal  effect  upon  them. 

I  have  enclosed  ichneumons  of  the  genus  Paniscus 
in  a  glass  cylinder  containing  the  larvae.  The  latter 
showed  not  the  slightest  sign  of  any  knowledge  of 
the  presence  of  their  deadly  foes,  until  accidentally 
touched  by  the  ichneumons  as  they  were  harrying 
up  and  down  in  their  endeavours  to  escape.  The 
instant  the  larvae  were  touched  they  assumed  the 
terrifying  attitude  and  turned  towards  the  spot,  the 
lips  of  the  opening  of  the  gland  swollen  by  pressure 
from  within,  in  readiness  for  an  immediate  discharge. 
When  an  ichneumon  was  held  in  the  forceps  and  thus 
made  to  touch  the  caterpillar  several  times,  the  fluid 
was  ejected  almost  instantly,  while  the  larva  also 
made  vigorous  efforts  to  bite  its  enemy  with  its 
powerful  mandibles.  A  little  of  the  secretion  was 
collected  in  a  tube  and  placed  on  the  ichneumons, 
which  collapsed  at  once,  and  either  died  or  took  many 
hours  to  recover. 

When  once  the  eggs  are  fixed  the  larva  is  doomed  ; 
the  maggots  begin  sucking  its  juices  as  soon  as  their 
heads  emerge  from  the  egg-shell,  while  the  tail  remains 


COMBINATION  OF  MANY  METHODS  OF  DEFENCE      277 

firmly  adherent  in  the  latter.  They  are  thus  tightly 
fixed  to  the  larva  by  both  ends.  The  caterpillar  is 
nearly  always  allowed  to  become  full  grown  and  spin 
a  cocoon  before  the  maggots  have  become  large.  In 
this  way  the  latter  secure  a  safe  retreat  and  more 
abundant  food.  When  they  have  grown  large  and 
their  prey  is  shrivelled  and  almost  dead,  they  lose  the 
attachment  to  the  egg-shell  and  devour  from  all  points, 
until  nothing  but  a  dry  and  empty 'skin  is  left.  They 
then  spin  their  own  cocoons  within  that  of  the  cater- 
pillar. The  latter  is  also  attacked  by  other  parasites 
and  probably  often  by  vertebrate  insect-eaters. 


A  well-protected  larva  is  often  especially  liable 
to  attack 

Thus,  in  spite  of  the  fact  that  the  caterpillar  pos- 
sesses so  many  defensive  appliances,  it  is  especially 
liable  to  attack,  far  more  so  than  many  other  larvae 
which  are  less'  protected.  Mr.  G.  C.  Bignell  enu- 
merated seven  species  of  parasites  which  attack  it.  At 
first  sight  this  seems  to  be  a  difficulty,  but  we  must  re- 
member that  we  are  probably  dealing  with  an  animal 
which  has  been  especially  attacked  for  a  long  period 
of  time,  and  which  has  been  saved  from  extermination 
by  the  repeated  acquisition  of  new  defensive  measures. 
But  any  improvement  in  the  means  of  defence  has 
been  met  by  the  greater  ingenuity  or  boldness  of  foes ; 
and  so  it  has  come  about  that  many  of  the  best  pro- 


278  THE   COLOURS   OF  ANIMALS 

tected  larvaB  are  often  those  which  die  in  the  largest 
numbers  from  the  attacks  of  enemies.  The  excep- 
tional standard  of  defence  has  been  only  reached 
through  the  pressure  of  an  exceptional  need. 


The  larva  of  Lobster  Moth  well  concealed  by  Special 
Protective  Resemblance 

The  caterpillar  which  I  select  as  a  second  example 
of  the  way  in  which  various  modes  of  defence  may  be 
combined,  is  that  of  the  Lobster  Moth  (Stauropun 
fagi),  which  is  rare  in  this  country.  Its  usual  food- 
plant  is  beech,  and  when  at  rest  it  is  well  concealed 
by  resembling  a  withered  leaf  irregularly  curled  up. 
The  stalk  is  represented  by  two  long  thin  appendages, 
which,  like  the  fork  of  the  Puss  caterpillar,  have  been 
modified  from  the  last  pair  of  claspers.  At  rest,  these 
appendages  are  held  together  and  appear  to  be  one. 
The  second  and  third  pairs  of  true  legs  are  extra- 
ordinarily long,  but  the  length  of  each  is  halved  by 
doubling  in  the  middle,  and  all  four  doubled-up  legs 
hang  down  in  a  bunch.  They  thus  resemble  in  the 
most  remarkable  manner  the  bunches  of  brown  scales 
(the  stipules  of  the  foliage  leaves)  which  enclose  the 
buds  of  the  beech,  and  hang  down  after  the  latter  are 
unfolded.  The  colour,  length,  and  shape  of  each 
folded  leg,  and  the  number  of  legs  which  thus  hang 
down  together,  are  all  such  as  strongly  to  suggest  the 
appearance  of  the  scales. 


COMBINATION  OF  MANY  METHODS  OF  DEFENCE      279 

The  same  larva  assumes  a  terrifying  attitude  (mimetic 
of  a  spider)  when  disturbed 

As  soon  as  the  larva  is  disturbed  it  holds  the 
anterior  part  erect,  and  assumes  a  terrifying  position 
which  mimics  that  of  a  large  spider.  All  the  points 
in  a  spider's  attitude  and  appearance  which  impress 
the  imagination  are  seized  upon  by  the  larva  and 
exaggerated  for  the  sake  of  effect,  while  quite  novel 
touches  are  added  with  the  same  object.  The  first 
pair  of  legs,  which  are  not  unusually  long,  are  held 
so  as  to  suggest  the  jaws  of  a  spider,  but  they  are 
larger  and  more  widely  gaping  than  any  actual  jaws. 
The  four  elongated  legs  are  held  widely  apart  and 
are  made  to  quiver  in  the  most  terrific  manner,  as  if 
the  animal  was  preparing  to  seize  its  prey.  The  hind 
part  of  the  body  is  turned  so  far  over  the  head  that 
the  two  appendages  project  over  it,  and  they  are  at 
the  same  time  made  to  diverge.  In  this  position  they 
strongly  suggest  the  appearance  of  a  pair  of  antennae, 
and  add  an  ideal  finish  to  the  apparent  monster, 
which  is,  indeed,  exactly  like  nothing  upon  earth,  but 
which  is,  nevertheless,  most  effective  in  its  appeal  to 
the  imagination.  When  the  hind  part  is  thus  turned 
forward,  its  ventral  surface  of  course  becomes  the 
dorsal  surface  of  the  abdomen  of  the  supposed  spider, 
and  it  is  appropriately  coloured  and  has  an  appearance 
of  plumpness  which  greatly  adds  to  the  resemblance. 
When  the  larva  is  much  irritated,  it  gently  moves 


280         THE  COLOURS  OF  ANIMALS 

this  hinder  part  from  side  to  side,  and  with  it  the 
antenna-like  appendages.  .  This  movement  also  adds 
to  the  general  effect. 

When  the  larva  is  slightly  irritated,  the  position  is 
often  imperfectly  assumed  at  first,  but  as  the  irritation 
is  repeated  and  increased,  the  animal  adds  the  various 
details  which  go  to  make  up  the  terrifying  attitude  in 
its  most  perfect  and  elaborate  form. 


Experimental  proof  of  the  protective  value  of  the 
terrifying  attitude  in  the  Lobster  caterpillar 

I  offered  two  of  these  larvae  to  the  marmoset,  and 
the  results  proved  the  importance  of  conducting  such 
experiments  with  the  greatest  care,  if  reliable  con- 
clusions are  to  be  obtained.  The  marmoset  knew 
that  my  boxes  contained  insects,  and  was  always  very 
keen  and  excited  at  the  sight  of  them.  When  the  box 
containing  one  of  the  '  Lobsters  '  was  opened,  the  cater- 
pillar was  seized  and  devoured  before  it  had  time  to 
alter  its  position,  and  before  the  marmoset  could  have 
had  the  chance  of  being  intimidated.  The  second 
caterpillar  was  placed  on  the  table  and  made  to  assume 
its  terrifying  attitude,  and  then  the  marmoset  was 
allowed  to  approach  it.  Although  a  caterpillar  of  the 
same  size  had  just  been  eaten  without  the  slightest 
hesitation,  the  marmoset  was  much  impressed  by  the 
alarming  sight,  and  only  ventured  to  attack  after  the 
most  careful  examination,  and  even  then  in  the  most 


COMBINATION  OF  MANY  METHODS  OF  DEFENCE      281 

cautious  manner.  However,  as  no  resistance  was  met 
with,  the  larva  was  soon  devoured  and  greatly  relished. 
I  then  tried  a  similar  experiment  with  a  lizard,  which 
only  attacked  the  larva  after  a  cautious  examination. 

The  interpretation  of  the  attitude  assumed  by 
the  irritated  caterpillar  was  originally  offered  by  H. 
Miiller,  and  it  may  be  now  said  to  rest  upon  a  basis 
of  experimental  proof.  It  is  also  very  likely  that  the 
spider-like  appearance  is  a  defence  against  the  insect 
enemies  of  S.  fagi.  This  is  rendered  very  probable  by 
H.  Miiller's  observation,  that  ichneumons  keep  out  of 
the  way  of  spiders  and  are  rarely  seen  in  their  webs. 


The  Lobster  caterpillar  also  deceptively  suggests  that  it 
has  been  already  stung  by  an  insect  parasite 

But  the  caterpillar  possesses  another  method  of 
defence,  if  hard  pressed  by  an  insect  foe.  On  the  side 
of  each  of  the  fourth  and  fifth 
body-rings  there  is  an  in- 
tensely black  patch  sunk  below 
the  general  surface  and  con- 
cealed by  a  triangular  flap. 
"When  irritated,  the  flap  is  FIG.  62.—  The  4th  and  sth  body- 

rings  (1st  and  2nd  abdominal) 


lowered  and  the  black  patches 

seen  from  the  right  side  when 


become  very  conspicuous  (see 

fig.  62).    It  is  probable,  as  H.       SaSWfSfcSS.  0Tniy 


•»r-n          i.  A    j        ii.    L          indicated  in  the  posterior  part 

Muller     has      Suggested,      that          of  the  5th  body-ring. 

these    marks   serve    to   imitate    the    appearance   of 


282         THE  COLOURS  OF  ANIMALS 

ichneumon  stings,  or  perhaps  the  result  of  a  struggle 
with  some  insect  enemy,  in  which  the  larva  has  been 
wounded.  The  blood  of  caterpillars  forms  a  black  clot, 
so  that  wounds  are  nearly  always  black  until  after 
the  next  change  of  skin. 

This  is  another  form  of  mimetic  resemblance — the 
deceptive  appearance  of  the  traces  left  by  an  enemy 
suggesting  that  the  larva  is  already  '  occupied.' 

The  larva  of  Stauropus  fagi  therefore  bristles  with 
defensive  structures  and  methods.  At  rest,  it  is  con- 
cealed by  a  combination  of  the  most  beautiful  Protec- 
tive Eesemblances  to  some  of  the  commonest  objects 
which  are  characteristic  of  its  food-plant.  Attacked, 
it  defends  itself  by  a  terrifying  posture,  made  up 
of  many  distinct  and  highly  elaborate  features,  all 
contributing  to  this  one  end.  Further  attacked,  it 
reveals  marks  which  suggest  that  it  can  be  of  no 
interest  to  an  insect  enemy,  for  another  parasite  is 
already  in  possession. 


The  failure  of  this  combination  of  defensive  methods 

The  caterpillar  is  so  rare  in  this  country  that  we 
know  but  little  of  the  enemies  which  attack  it.  Two 
parasites  are,  however,  mentioned  in  Mr.  Bignell's  list. 
Its  very  rarity,  however,  proves  the  constant  failure  of 
all  defensive  measures.  There  is  little  doubt  that  the 
larva  is  in  the  same  position  as  that  of  the  Puss  Moth, 


COMBINATION  OF  MANY  METHODS  OF  DEFENCE     283 

but  has  not  been  equally  successful.  The  means  of 
defence  have  been  the  response  on  the  part  of  the 
organism  to  the  increasing  attacks  of  enemies,  and 
the  latter  on  their  part  have  met  the  response  by 
increased  vigilance,  activity  or  boldness.  Mr.  Belt's 
metaphor  of  the  mutual  selective  action  between  dogs 
and  hares  exactly  explains  the  relation  between  these 
highly-protected  larvae  and  their  enemies,  and  serves 
to  show  why  it  is  that  less  attacked  larvae  are  also 
less  defended  (see  pp.  253-55). 

When  we  compare  the  elaborate  defence  of  these 
two  much-persecuted  larvae,  with  the  far  simpler  and 
less  effective  protection  of  many  caterpillars  which 
are  less  subject  to  attack,  we  are  made  to  realise  the 
pre-eminence  of  natural  selection  in  moulding  the 
forms  of  life  around  us  for  their  ceaseless  mutual 
Btrifc. 


284         THE  COLOUES  OF  ANIMALS 


CHAPTER  XV 

COLOURS  PRODUCED  BY   COURTSHIP 

IN  addition  to  the  colours  and  patterns  which  assist 
an  animal  to  evade  or  warn  off  its  enemies  or  to  secure 
its  prey,  there  are  also  colours  arid  appendages  which 
must  have  some  very  different  meaning.  These  ap- 
pearances are  seen  in  mature  animals,  and  frequently 
undergo  periodical  development  at  times  which  cor- 
respond to  the  breeding  season;  and  when  the  two 
sexes  differ,  the  males  are  almost  invariably  the  more 
brilliant.  Although  far  less  important  and  wide-spread 
than  the  protective  or  aggressive  colours,  they  are 
more  generally  known  and  appreciated,  because  they 
are  conspicuous  as  well  as  beautiful,  and  are  freely 
displayed  by  the  animals  which  possess  them. 

The  theory  of  Sexual  Selection 

However  these  colours  may  have  arisen,  every  ob- 
server must  admit  that  they  are  in  some  way  connected 
with  sex.  Darwin  accounted  for  them  by  his  celebrated 
theory  of  *  Sexual  Selection.' '  He  supposed  that 

1  The  Descent  of  Man,  Part  ii.  Sexual  Selection. 


COLOURS  PRODUCED  BY  COURTSHIP  285 

the  aesthetic  sense  is  widely  distributed  among  the 
higher  animals  (vertebrates  and  some  of  the  most 
specialised  invertebrates),  and  that  the  colours  which 
certainly  appeal  to  this  sense  in  man,  are  not  without 
effect  in  causing  gratification  to  the  animals  them- 
selves. Among  the  other  forms  of  rivalry  between  the 
males  for  the  possession  of  the  females,  there  is  rivalry 
in  beauty  and  its  appropriate  display ;  and  the  choice 
of  the  females  being  largely  determined  by  their 
aesthetic  preferences,  the  beauty  and  agility  of  the 
males  has  been  gradually  increased.  The  females 
may  share  in  the  growing  adornment,  for  the  qualities 
of  the  male  will  tend  to  pass  over  by  degrees  into  the 
female  offspring,  although  such  tendencies  will  be 
often  checked  by  the  operation  of  natural  selection, 
as  Mr.  Wallace  has  shown  us  in  a  most  convincing 
manner.1 

This  explanation  of  the  origin  and  meaning  of 
sexual  colouring  is  not  accepted  by  Mr.  Wallace, 
Darwin's  great  compeer  in  the  discovery  of  the  fruit- 
ful principle  of  natural  selection,  and  he  brings  forward 
many  difficulties,  and  suggests  alternative  explanations 
in  his  recent  work  on  '  Darwinism.' 

It  is  of  course  quite  impossible  to  discuss  this 
most  interesting  and  difficult  subject  in  any  adequate 
manner  within  the  limits  of  the  present  work.  This 
volume  would,  however,  be  incomplete  without  some 

1  Darwinism,  1st  edit.  chap.  x.  pp.  268-300.  Further  allusions  to 
Mr.  Wallace's  views  on  the  subject  refer  to  this  chapter  of  his  work. 


286         THE  COLOURS  OF  ANIMALS 

account  of  the  subject;  and  furthermore  there  are 
certain  recent  observations  which  seem  to  me  to  yield 
strong  support  to  Darwin's  theory. 


Insufficient  evidence  for  existence  of  aesthetic  preferences 

Mr.  Wallace's  chief  objection  is  the  lack  of  evi- 
dence that  the  female  has  any  aesthetic  preferences  at 
all  in  the  selection  of  her  mate.  When,  however,  he 
admits  that  display  of  their  decorative  plumage  by 
male  birds  is '  demonstrated,'  and  that  the  females  are 
in  all  probability  '  pleased  or  excited  by  the  display,' 
he  certainly  admits  the  possession  of  an  aesthetic 
sense ;  while  the  insufficient  evidence  that  the  final 
choice  of  the  female  is  frequently  determined  by  the 
gratification  of  this  sense,  may,  I  think,  be  chiefly  due 
to  want  of  patient  or  discriminating  observations  upon 
wild  animals  in  their  natural  conditions. 


Reasons  for  the  lack  of  evidence 

It  is  a  very  remarkable  fact  that  the  great  impetus 
given  to  biological  inquiry  by  the  teachings  of  Darwin 
has  chiefly  manifested  itself  in  the  domain  of  Com- 
parative Anatomy,  and  especially  in  that  of  Embry- 
ology, rather  than  in  questions  which  concern  the 
living  animal  as  a  whole  and  its  relations  to  the  organic 
world.  And  yet  these  were  the  questions  in  which 
Darwin  himself  was  principally  interested. 


COLOURS  PRODUCED  BY  COURTSHIP  287 

Sexual  Selection  is  still  to  some  extent  subjudice, 
simply  because  the  vast  majority  of  those  interested 
in  nature  are  either  anatomists,  microscopists,  syste- 
matists,  or  collectors.  There  are  comparatively  few 
true  naturalists — men  who  would  devote  much  time 
and  the  closest  study  to  watching  living  animals  amid 
their  natural  surroundings,  and  who  would  value  a 
fresh  observation  more  than  a  beautiful  dissection  or 
a  rare  specimen.  I  trust  that  it  may  not  be  supposed 
that  I  in  any  way  undervalue  the  immense  importance 
of  these  other  subjects ;  but  there  are  certain  problems 
which  they  can  never  solve,  and  Sexual  Selection  is 
one  of  these. 


The  only  reliable  evidence  on  this  subject  can  be  obtained 
frcm  the  study  of  wild  animals  in  their  natural  sur- 
roundings 

Some  of  the  most  beautiful  sexual  colours  are 
found  among  the  butterflies,  and  the  males  are  fre- 
quently far  more  brightly  coloured  than  the  females. 
Mr.  Wallace  has  pointed  out  that  the  only  direct 
evidence  is  opposed  to  the  theory  that  any  choice  is 
exercised  by  the  females.  The  evidence  depends  upon 
the  observations  of  several  entomologists  upon  moths, 
and  especially  those  of  Dr.  Alexander  Wallace,  of  Col- 
chester, upon  Bombyx  cynthia.  The  strength  of  this 
evidence  is  much  shaken  by  the  fact  that  the  moths 
were  bred  in  captivity,  and  I  think  that  the  question 


288  THE  COLOURS   OF  ANIMALS 

can  only  be  settled  by  careful  observation  under  the 
most  natural  conditions.  This  conclusion  is  rendered 
probable  by  the  following  considerations. 

The  female  of  the  Emperor  Moth  (Saturnia  carpini) 
is  so  eagerly  sought  by  the  males,  that  when  a  virgin 
female  is  taken  into  a  favourable  locality  the  collector 
is  soon  surrounded  by  troops  of  males  which  have 
been  guided  by  a  marvellously  delicate  sense  of  smell 
residing  in  their  branching  antennae.  So  delicate  is 
the  sense  that  the  female  is  recognised  perhaps  miles 
away,  and  recognised  as  a  virgin.  Directly  mating 
takes  place  the  other  males  disappear.  In  this  case 
selection  chiefly,  if  not  entirely,  tends  to  improve  the 
sense  of  smell  in  the  males  and  the  mode  and  rapidity 
of  their  flight.  The  mode  of  flight  is  probably  im- 
portant in  enabling  the  insect  to  cover  as  wide  a 
volume  of  air  as  possible  while  it  advances,  and  thus 
to  stand  a  greater  chance  of  crossing  some  thin 
stratum  or  current  of  air  in  which  the  odoriferous 
particles  are  contained.  To  such  a  selective  process 
we  must  ascribe  the  wonderful  antennae  of  these 
males  and  their  peculiar  and  rapid  flight.  Since, 
however,  both  males  and  females  are  very  beautiful, 
the  males  possessing  the  brighter  colours,  this 
example  seems  at  first  sight  to  support  Mr.  Wallace's 
views.  I  shall  endeavour  to  show  that  the  facts  are 
capable  of  an  opposite  interpretation.  I  have  here 
called  attention  to  the  habits  of  the  species,  because 
it  is  nearly  allied  to  Bombyx  cynthia,  and  because  the 


COLOURS  PRODUCED  BY  COURTSHIP     289 

keenness  of  the  males  in  pursuing  the  females  is  so 
well  known  and  remarkable, 

In  spite  of  this  very  exceptional  keenness  in  the 
wild  state,  my  friend  Dr.  Dixey  found  in  two  succes- 
sive years  that  it  is  by  no  means  easy  to  pair  them, 
when  both  males  and  females  are  bred  in  captivity. 
I  have  had  exactly  the  same  experience  with  the  con- 
tinental Tau  Emperor  (Aglia  tau),  although  the 
wonderful  antennae  of  the  male  show  that  the  powers 
of  this  species  are  even  more  intense  than  those  of  our 
own  Emperor  Moth.  If  there  is  such  a  marvellous 
change  in  the  disposition  of  these  species,  it  is  at  least 
probable  that  similar  changes  occur  in  other  species 
with  more  phlegmatic  males.  The  difficulty  with 
which  the  great  majority  of  butterflies  and  moths  can 
be  induced  to  pair  when  bred  in  captivity  (although 
captured  females,  already  fertilised,  will  generally 
lay  eggs),  and  the  fact  that  an  increased  chance  of 
success  is  afforded  by  imitating  the  natural  conditions 
as  far  as  possible,  point  in  the  same  direction. 

The  argument  applies  with  even  greater  force  to 
many  of  the  higher  animals.  The  effect  of  domestica- 
tion upon  the  brain  of  the  domestic  duck  has  been 
proved  in  the  most  striking  manner  by  Sir  James 
Crichton  Browne.1  The  comparison  between  twenty 

1  The  interesting  facts  and  conclusions  summarised  on  p.  290  were 
contained  in  a  paper  read  at  the  meeting  of  the  British  Association 
at  Sheffield  in  1879.  The  paper  has  never  been  published,  but  Sir 
James  Crichton  Browne  has  kindly  allowed  me  to  use  the  manu- 
script. 


290  THE  COLOURS   OF  ANIMALS 

wild  and  twenty  domestic  ducks  showed  that  the  brain 
of  the  former  is,  in  proportion  to  the  weight  of  the 
body,  nearly  twice  as  heavy  as  that  of  the  latter. 
The  average  weights  were  as  follows  :  — 

Domestic  duck         .        .     1816-768  grammes 
Brain  of        „  „  .        .          5-370 

Wild  duck        .        .        .    1155-813 
Brain  of      „        „          ...          6-433        „ 
Brain  weight  to  body  weight  as  1  to  338-318  in  domestic  duck 
1  to  179-669  in  wild  duck. 

These  results  were  confirmed  by  the  examination  of 
over  sixty  individuals,  in  addition  to  the  forty  alluded 
to  above. 

The  effects  of  this  degeneration  are  seen  in  the 
fact  that  the  '  wild  duck  is,  from  first  to  last,  a  superior 
being,  mentally  considered,  and  exhibits  an  amount  of 
intellectual  and  instinctive  acuteness,  and  force  and 
independence  of  character,  to  which  the  barn-door 
variety  can  make  no  pretension.'  A  careful  com- 
parison of  the  habits  and  instincts  of  the  type  with 
those  of  the  domestic  race,  shows  that  '  altogether 
there  is  a  mental  sprightliness  and  momentum  in  the 
wild  duck  that  have  no  counterparts  in  its  domestic 
congener.'  The  domestic  duck,  ever  since  its  first 
subjugation  by  man,  '  for  eighteen  centuries,  and  not- 
withstanding occasional  infusions  of  wild  blood,  has 
been  sinking  into  imbecility.' 

These  facts  are  also  true  of  many  other  domesti- 
cated animals,  and  they  serve  to  indicate  that  Sexual 
Selection  can  only  be  tested  fairly  by  the  observation 


COLOURS  PRODUCED   BY   COURTSHIP  291 

of  wild  forms.  This  is  even  the  case  with  the  few 
races  which  have,  perhaps,  been  raised  by  domestica- 
tion to  a  higher  intellectual  level;  for  the  mental 
development  which  has  been  induced  by  artificial 
selection  has  reference  to  the  requirements  or  fancies 
of  man,  rather  than  to  the  necessities  of  the  species. 


The  '  Assembling '  of  male  Moths 

In  many  species  of  moths  the  males  '  assemble ' 
round  the  freshly  emerged  female,  but  no  special 
advantage  appears  to  attend  an  early  arrival.  .The 
female  sits  apparently  motionless  while  the  little 
crowd  of  suitors  buzz  around  her  for  several  minutes. 
Suddenly,  and,  as  far  as  one  can  see,  without  any  sign 
from  the  female,  one  of  the  males  pairs  with  her  and 
all  the  others  immediately  disappear. 

In  these  cases  the  males  do  not  fight  or  struggle 
in  any  way,  and  as  one  watches  the  ceremony  the 
wonder  arises  as  to  how  the  moment  is  determined, 
and  why  the  pairing  did  not  take  place  before.  All 
the  males  are  evidently  most  eager  to  pair,  and  yet 
when  pairing  takes  place  no  opposition  is  offered  by 
the  other  males  to  the  successful  suitor.  Proximity 
does  not  decide  the  point,  for  long  beforehand  the 
males  often  alight  close  to  the  female  and  brush 
against  her  with  fluttering  wings. 

In  watching  this  wonderful  and  complicated  court- 
ship, one  is  driven  to  the  conclusion  that  the  female 


292         THE  COLOURS  OF  ANIMALS 

must  signify  her  intention  in  some  way  unknown  to 
us,  and  that  it  is  a  point  of  honour  with  the  males  to 
abide  by  her  decision. 

I  have  watched  the  process  exactly  as  I  have  de- 
scribed it  hi  a  common  northern  Noctua,  the  Antler 
Moth  (Charaas  graminis),  and  I  have  seen  the  same 
thing  among  beetles.  The  fact  is  well  known  to  ento- 
mologists, and,  as  far  as  the  evidence  goes,  it  supports 
Darwin's  theory. 

The  females  of  certain  Butterflies  more  beautiful  than 
the  males 

Another  class  of  facts  quoted  by  Darwin  is  barely 
alluded  to  by  Wallace ;  but  I  think  that  it  will  be  of 
the  utmost  importance  in  deciding  this  question  when 
further  and  more  detailed  observations  are  made. 

The  females  of  many  butterflies  are  more  beautiful 
than  the  males,  and  then  '  the  plainer  males  closely 
resemble  each  other,  showing  that  here  the  females 
have  been  modified ;  whereas  in  those  cases  where  the 
males  are  the  more  ornate,  it  is  those  which  have 
been  modified,  the  females  remaining  closely  alike.' l 
Many  examples  are  found  among  our  British  butter- 
flies, e.g.  the  Meadow  Brown,  the  Clouded  Yellow, 
and  the  Whites.  The  females  of  such  species  support 
the  males  during  the  marriage  flight,  while  the  oppo- 
site is  known  to  occur  in  many  other  butterflies.  It 

1  Darwin  loc.  cit.  1874,  p.  318. 


COLOURS  PRODUCED   BY   COURTSHIP  293 

is  therefore  probable  that  the  females  take  the  more 
active  share  in  the  wooing,  and  that  the  males  have 
exercised  their  aesthetic  preferences,  and  have  thus 
caused  their  mates  to  be  more  beautiful  than  them- 
selves. These  striking  facts  were  brought  before  Mr. 
Darwin  by  Professor  Meldola,  who  informs  me  that 
he  has  confirmed  the  facts  by  his  own  observation  in 
the  field. 

During  the  past  summer  (1889)  I  have  seized  every 
available  opportunity  of  watching  the  wooing  of  our 
common-  white  butterflies  (Pieris.  brassicce,  P.  rap<e, 
and  P.  napi),  and  I  can  quite  confirm  Professor 
Meldola's  prediction.  The  females  were  far  more 
ardent  than  the  males,  and  when  the  courtship  came 
to  an  abrupt  termination,  as  it  generally  did,  it  was 
invariably  due  to  the  coyness  of  the  males.  These 
facts  strongly  support  the  opinion  that  the  beauty  of 
the  females  has  been  gradually  produced  by  the  pre- 
ferences of  the  males.1 


1  S.  B.  J.  Skertchly  has  recently  (Ann.  and  Mag.  Nat.  Hist.  Sept. 
1889,  pp.  209  et  seq.)  described  a  case  in  which  the  rare  female  of 
Ornithoptera  brookeana  eagerly  and  persistently  courted  a  male, 
although  males  are  more  abundant  and  far  more  brilliantly  coloured. 
Professor  Moseley,  on  the  other  hand,  describes  the  courtship  of 
Ornithoptera  poseidon  in  the  following  words :— '  I  once  .  .  .  was 
lucky  enough  to  find  a  flock  of  about  a  dozen  males,  fluttering  round 
and  mobbing  a  single  female.  They  were  then  hovering  slowly, 
quite  close  to  the  ground,  and  were  easily  caught.  The  female  had 
thus  a  large  body  of  gaudy  admirers  from  which  to  make  her  choice.' 
(A  Naturalist  on  the  '  Clmllenger,'1  p.  373.)  The  wide  difference  be- 
tween these  two  accounts  of  courtship  in  closely  allied  species,  proves 
the  importance  of  making  many  observations  before  we  can  hope  to 
14 


294         THE  COLOURS  OF  ANIMALS 


Disappearance  of  the  beauty  of  males  when  the 
females  become  degenerate 

I  will  now  return  to  the  Emperor  Moth,  and 
attempt  to  show  how  its  bright  colours  can  be  ex- 
plained by  the  theory  of  Sexual  Selection.  In  its 
present  condition  the  female  is  certainly  passive,  and 
probably  always  accepts  the  attention  of  the  first  male 
to  arrive.  The  antennae,  which  are  so  wonderfully 
complex  in  the  males,  are  simple  and  rudimentary  in 
the  female,  and  probably  valueless  as  sense  organs. 
We  must  therefore  believe  that  the  conditions  which 
produced  the  bright  colours  and  patterns  are  now  at 
an  end,  and  that  their  disappearance  is  only  a  question 
of  time.  And  there  is  evidence  for  both  these  con- 
clusions. 

If  we  examine  the  female  chrysalis,  the  antennae 
are  seen  to  be  large  and  well- formed,  and  altogether 
out  of  proportion  to  the  slender  thread-like  organs 
which  are  formed  within  them.  The  antennae  have 
dwindled  in  the  moth,  but  BO  recently  that  the  pupal 
organs  within  which  they  are  formed  have  undergone 
but  slight  diminution,  if  any  at  all.  This  most  inter- 
esting fact  was  brought  before  my  notice  by  Professor 
Moseley.  Here  then  we  have  the  clearest  evidence 

reach  a  safe  conclusion.  Professor  Moseley's  account  is,  however 
supported  by  o.  large  number  of  observations  upon  other  species,  in 
which  the  relation  between  the  sexe«  resembles  that  obtaining  in 
Ornithoptera, 


COLOURS  PRODUCED  BY   COURTSHIP  295 

that  the  female  Emperor  was  very  different  from  the 
inert  creature  I  have  described.  In  the  full  posses- 
sion of  her  faculties,  she  doubtless  took  that  intelligent 
interest  in  courtship  which  is  to  ba  expected  of  every 
properly  endowed  female. 

I  have  also  maintained  that  under  these  circum- 
stances the  colours  are  likely  to  disappear.  Such  a 
conclusion  can  be  tested  by  examining  other  species 
in  which  the  degeneration  of  the  female  is  more 
complete,  and  has  doubtless  occupied  a  far  longer 
time. 

In  another  genus  of  Bombyces  (Orgyia),  some  of 
the  females  (of  which  the  common  Vapourer  Moth  is 
an  example)  are  far  more  degenerate.  They  never 
leave  the  cocoon,  but  lay  their  eggs  all  over  it ;  their 
antennae  and  wings  are  rudimentary.  The  male,  on 
the  other  hand,  flies  actively  about  and  has  enormously 
developed  antenna?.  Success  in  courtship  is  almost 
certainly  a  mere  question  of  speed  and  keen  scent.1 
In  this  case  the  male  is  very  plainly  coloured  in 
various  shades  of  brown,  but  he  still  retains  a  trace 
of  his  vanished  beauty  in  a  white  spot  in  the  centre 
of  each  fore  wing.  An  examination  of  the  pupa  shows 
us  that  the  female  once  possessed  larger  .wings  and 
more  perfect  sense  organs. 

In  Psyche  and  allied  genera  the  change  has  pro- 

1  Mr.  E.  B.  Titchener  tells  me  that  this  is  not  always  the  case; 
for  a  female  in  his  possession  refused  the  first  male  which  arrived. 
The  usual  experience  with  the  Emperor  Moth,  &c.,  seems  to  indicate 
that  such  an  exception  is  very  rare. 


296         THE  COLOURS  OF  ANIMALS 

ceeded  much  farther  in  the  same  direction.  In  the 
most  degenerate  species  the  female  is  a  mere  bag  of 
eggs,  without  limbs  or  sense  organs ;  she  does  not 
even  leave  the  pupa-case,  but  thrusts  out  the  end  of 
her  body  that  fertilisation  may  take  place.  In  the  pupa- 
case  of  the  most  degenerate  forms,  no  distinct  trace  of 
former  organs  can  be  made  out,  but  in  that  of  certain 
closely  allied  species  they  can  still  be  recognised, 
although  in  a  very  rudimentary  condition;  in  others 
again,  still  more  distinctly.  In  the  extreme  forms 
the  degeneration  of  the  female  has  proceeded  as  far 
as  it  is  possible  to  go,  and  in  all  it  must  be  excessively 
ancient.  The  males  of  nearly  all  Psycldda  are  cha- 
racterised by  a  uniform  sombre  colour  of  a  brown  or 
grey  tint ;  all  bright  colours  and  all  traces  of  pattern 
are  almost  invariably  absent. 

The  successive  degrees  of  degeneration  and  atten- 
dant loss  of  colour  by  the  males  have  been  traced  in 
species  all  of  which  belong  to  the  Bombyces;  the 
males  are  in  all  cases  day-flying.  The  day-flying 
Bombyces,  in  which  the  females  retain  full  possession 
of  their  faculties,  are  remarkable  for  the  brightness 
and  beauty  of  their  colours,  and  this  is  true  of  species 
which  are  probably  without  any  special  protection  by 
a  disagreeable  taste  or  smell. 

The  condition  presented  by  the  Psychidce  was  sug- 
gested to  me  by  my  friend  Mr.  W.  White.  I  could  give 
many  details  which  seem  to  explain  the  cause  of  the 
degeneration,  but  this  is  unnecessary  for  the  present 


COLOURS  PRODUCED   BY  COURTSHIP  297 

purpose.  The  comparison,  which  is,  I  believe,  now 
made  public  for  the  first  time,  appears  to  yield  a  very 
strong  support  to  the  views  of  Mr.  Darwin  on  this 
question. 

Sexual  Selection  tested  by  the  courtship  of  Spiders 

Mr.  Wallace  quotes  an  opinion  against  Sexual 
Selection  which  is  certainly  of  the  greatest  weight, 
that  of  our  eminent  authority  on  spiders,  the  Rev.  0. 
Pickard-Cambridge.1  I  am  therefore  especially  pleased 
to  be  able  to  refer  to  an  American  paper  which  has 
appeared  in  the  present  year  (1889),  describing  the 
most  careful  observations  upon  the  courtship  of 
spiders.2  As  the  result  of  their  investigations,  especi- 
ally directed  towards  the  solution  of  this  very  question 
of  the  existence  of  Sexual  Selection,  the  authors  come 
to  a  conclusion  which  is  the  opposite  of  that  drawn 
by  Mr.  Pickard-Cambridge. 

The  spiders  of  the  family  Attida,  which  were  the 
subjects  of  investigation,  appear  to  be  very  suitable  for 
the  purpose,  because  courtship  does  not  appear  to  be 
checked  or  modified  by  confinement,  as  it  is  in  so 
many  Lepidoptera.  The  amount  of  labour  spent  in 
this  admirable  piece  of  work  may  be  gathered  from 


1  Darwinism,  pp.  296-97. 

2  Occasional  Papers  of  the  Natural  History  Society  of  Wis- 
consin, vol.  i.  1889,  Milwaukee.      Observations  on  Sexual  Selection 
in  Spiders  of  the  Family  Attida,  by  George  W.  and  Elizabeth  G. 
Peckham. 


298         THE  COLOURS  OF  ANIMALS 

the  fact  that  the  authors  '  often  worked  four  or  five 
hours  a  day,  for  a  week,  in  getting  a  fair  idea  of  the 
habits  of  a  single  species.' 

The  courtship  of  Saitis  pulex  appears  to  be  a 
most  elaborate  affair.  A  male  was  placed  in  a  box 
containing  a  mature  female.  '  He  saw  her  as  she 
stood  perfectly  still,  twelve  inches  away ;  the  glance 
seemed  to  excite  him  and  he  moved  toward  her; 
when  some  four  inches  from  her  he  stood  still, 
and  then  began  the  most  remarkable  performances 
that  an  amorous  male 
could  offer  to  an  admir- 
ing female.  She  eyed 
him.  eagerly,  changing 
her  position  from  time 
to  time  so  that  he  might 
be  always  in  view.  He, 
raising  his  whole  body 
on  one  side  by  straight- 
FIG.  63.-saitu  puiex.  Male  dauciug  ening  out  the  legs,  and 

before  female  (from  Peckham). 

lowering  it  on  the  other 

by  folding  the  first  two  pairs  of  legs  up  and  under,  leans 
so  far  over  as  to  be  in  danger  of  losing  his  balance, 
which  he  only  maintained  by  sidling  rapidly  towards 
the  lowered  side.  The  palpus,  too,  on  this  side  was 
turned  back  to  correspond  to  the  direction  of  the  legs 
nearest  it  (see  fig.  63).  He  moved  in  a  semicircle 
for  about  two  inches,  and  then  instantly  reversed  the 
position  of  the  legs  and  circled  in  the  opposite  direc- 


COLOURS  PRODUCED  BY  COURTSHIP     299 

tion,  gradually  approaching  nearer  and  nearer  to  the 
female.  Now  she  dashes  towards  him,  while  he, 
raising  his  first  pair  of  legs,  extends  them  upward 
and  forward  as  if  to  hold  her  off,  but  withal  slowly 
retreats.  Again  and  again  he  circles  from  side  to 
side,  she  gazing  towards  him  in  a  softer  mood,  evi- 
dently admiring  the  grace  of  his  antics.  This  is  re- 
peated until  we  have  counted  111  circles  made  by  the 
ardent  little  male.  Now  he  approaches  nearer  and 
nearer,  and  when  almost  within  reach,  whirls  madly 
around  and  around  her,  she  joining  and  whirling  with 
him  in  a  giddy  maze.  Again  hie  falls  back  and  re- 
sumes his  semicircular  motions,  with  his  body  tilted 
over  ;  she,  all  excitement,  lowers  her  head  and  raises 
her  body  so  that  it  is  almost  vertical;  both  draw 
nearer ;  she  moves  slowly  under  him,  he  crawling 
over  her  head,  and  the  mating  is  accomplished. 
After  they  have  paired  once  the  preliminary  court- 
ship is  not  so  long.'  On  one  occasion  a  female  was 
the  more  eager  of  the  two,  but  this  is  evidently 
very  exceptional.  The  female  always  watches  the 
antics  of  the  male  intently,  but  often  refuses  him 
in  the  end,  '  even  after  dancing  before  her  for  a  long 
time.'  Such  observations  strongly  point  towards 
the  existence  of  female  preference  based  on  aesthetic 
considerations. 

In  Epiblemum  scenicum  '  the  females  seemed  to  have 
some  difficulty  in  choosing  from  among  the  males,  but 
after  a  decision  had  been  reached,  and  a  male  accepted, 


300  THE  COLOUES   OF  ANIMALS 

there  appeared  to  be  complete  agreement.'  Icius  sp.  was 
watched  for  hours  under  natural  conditions  as  well  as 
in  confinement.  '  A  dozen  or  more  males  and  about 
half  as  many  females  were  assembled  together  within 
the  length  of  one  of  the  rails.  The  males  were 
rushing  hither  and  thither,  dancing  opposite  now  one 
female  and  now  another ;  often  two  males  met  each 
other,  when  a  short  passage  of  arms  followed.  They 
waved  their  first  legs,  sidled  back  and  forth,  and 
then  rushed  together  and  clinched,  but  quickly  sepa- 
rated, neither  being  hurt,  only  to  run  off  in  search  of 
fairer  foes.' 

The  dangers  of  courtship  were  also  often  witnessed. 
A  male  of  Hasarius  Hoyi  continued  to  advance  after 
the  female  had  shown  signs  of  impatience,  '  when  she 
seized  him  and  seemed  to  hold  him  by  the  head  for  a 
minute,  he  struggling.  At  last  he  freed  himself  and 
ran  away.  This  same  male  after  a  time  courted  her 
successfully.'  The  male  of  Phidippus  rufus  was  caught 
and  eaten  when  he  insisted  upon  showing  off  his  fine 
points  too  persistently.  The  single  female  of  Phidippus 
morsitans  under  observation  '  was  a  savage  monster. 
The  two  males  that  we  provided  for  her  had  offered 
her  only  the  merest  civilities,  when  she  leaped  upon 
them  and  killed  them.'  The  first  pair  of  legs  are  long 
and  covered  with  white  hairs  in  the  male  :  '  it  was 
while  one  of  the  males  was  waving  these  handsome 
legs  over  his  head  that  he  was  seized  by  his  mate  and 
devoured.' 


COLOURS  PRODUCED  BY  COURTSHIP  301 

When  the  males  possess  any  special  adornments 
they  make  a  point  of  displaying  them  as  fully  as  pos- 
sible. The  male  of  Synageles  picata  (see  fig.  53,  page 
256)  has  the  first  pair  of  legs  especially  thickened  : 
'  these  are  flattened  on  the  anterior  surface,  and  are  of 
a  brightly  iridescent  steel-blue  colour.'  As  he  is  ap- 
proaching the  female  he  pauses  '  every  few  moments 
to  rock  from  side  to  side,  and  to  bend  his  brilliant  legs 
so  that  she  may  look  full  at  them ;  ...  he  could  not 


PIG.  64. — Habrocestum  splenderu  ;  position  of  male  approaching  female 
(from  Peckham) ;   x  about  8  or  9  times. 


have  chosen  a  better  position  than  the  one  he  took  to 
make  a  display.'  In  fact,  his  attitude  appears  to  have 
first  directed  the  attention  of  the  authors  to  his  pecu- 
liar beauty.  The  male  of  Dendryphantes  capita  tus  has 
a  bronze-brown  face,  rendered  conspicuous  by  snow- 
white  bands,  and,  whether  intentionally  or  not,  he 
assumes  an  attitude  which  serves  admirably  to  expose 
this  feature  to  the  attentive  female.  This,  however, 
is  by  no  means  his  only  charm,  and  his  '  antics  are 
repeated  for  a  very  long  time,  often  for  hours,  when  at 


302 


THE  COLOURS  OF  ANIMALS 


.      . — 
of  male  approaching  female  (from  Peckham). 


last  the  female,  either  won  by  his  beauty  or  worn  out 
by  his  persistence,  accepts  his  addresses.'      In  the 

male  of  Habroces- 
tum  splendens  the 
abdomen  is  of  a 
magnificent  pur- 
plish red,  and  he 
assumes  an  atti- . 
tude  which  displays 
this  beauty  very 
completely  (see 
fig.  64). 

The  case  of 
Astia  vittata  is  es- 
pecially interesting, 
because  there  are 
two  well  marked 
varieties  of  male, 
one  red  like  the 
female,  and  the 
other  black,  with 
three  tufts  of  hair 
on  the  cephalo- 
thorax.  The  two 
forms  pass  into  each 
other,  although  the 
tufts  only  occur  in 

the  fully  developed  niger  form.      The  attitudes  and 
movements  of  courtship  are  entirely  different  in  the 


FIG.  66.— Astia  vittata,  var.  niger ;  position  of 
black  variety  of  male  approaching  female  (from 
Peckham). 


COLOURS  PRODUCED  BY  COURTSHIP     303 

two  varieties  (compare  figs.  65  and  66) :  '  the  niger 
form,  evidently  a  later  development,  is  much  the  more 
lively  of  the  two,  and  whenever  the  two  varieties  were 
seen  to  compete  for  a  female,  the  black  one  was 
successful.'  It  must  be  admitted  that  these  facts 
afford  the  strongest  support  to  the  theory  of  Sexual 
Selection. 

I  have  quoted  much  from  this  important  paper 
because,  as  far  as  I  am  aware,  it  is  the  only  attempt 
to  solve  the  question  by  the  systematic  observation  of 
courtship  in  a  single  group  of  animals.  Many  other 
equally  interesting  and  significant  cases  are  also  re- 
corded, and  the  paper  is  profusely  illustrated  with 
representations  of  the  most  characteristic  attitudes. 
As  the  result  of  the  whole  body  of  observations  the 
authors  are  of  the  opinion  that '  in  the  Attidce  we  have 
conclusive  evidence  that  the  females  pay  close  attention 
to  the  love  dances  of  the  males,  and  also  that  they  have 
not  only  the  power,  but  the  will,  to  exercise  a  choice 
among  the  suitors  for  their  favour.'  Eemembering 
that  this  conclusion  has  only  been  reached  in  the 
Attidts  by  the  closest  study,  I  think  we  may  safely 
explain  the  smaller  confidence  with  which  we  can 
speak  of  other  animals  by  the  want  of  sufficiently 
careful  and  systematic  investigation. 


304      •   THE  COLOURS  OF  AKIMAL8 


Display  in  courtship  occurs  in  plainly  coloured  as  well 
as  in  ornamental  species 

In  speaking  of  the  display  of  decorative  plumage, 
Mr.  Wallace  remarks  :  *  It  is  very  suggestive  that  simi- 
lar strange  movements  are  performed  by  many  birds 
which  have  no  ornamental  plumage  to  display.'  The 
same  facts  are  probably  true  of  all  groups  of  animals 
in  which  the  males  of  certain  species  are  specially 
adorned.  It  was  certainly  the  case  with  spiders,  and 
the  '  assembling  '  of  the  males  of  the  sombre  Antler 
Moth  has  been  already  described. 

The  great  beauty  of  many  appearances  which  are, 
nevertheless,  of  extreme  importance  as  Protective 
Eesemblances,  is  doubtless  explicable  in  the  same 
manner.  It  is  likely  that  all  visible  parts  of  the 
organism,  even  those  with  a  definite  physiological 
meaning,  appeal  to  the  aesthetic  sense  of  the  opposite 
sex.  The  harsh  contrasts  and  gaudy  colours  of  warn- 
ing appearances,  and  the  sombre  tints  which  bring 
perfect  concealment,  must  alike  possess  a  meaning  in 
courtship,  but  the  tendency  towards  the  develop- 
ment of  higher  forms  of  beauty  is  rigorously  kept 
in  check  by  natural  selection.  Eemove  the  check  or 
render  it  less  exacting,  and  the  tendency  at  once 
manifests  itself  (see  pp.  311-13). 


COLOURS  PRODUCED  BY  COURTSHIP     305 


Such  facts  point  towards  the  existence  of  a  wide-spread 
aesthetic  sense  in  the  higher  animals 

All  such  facts  taken  together  seem  to  me  to  sup- 
port the  opinion  that  an  aesthetic  sense  exists  in  the 
females  of  all  groups  in  which  courtship  is  accompanied 
by  display  of  any  kind,  and  that  the  males  vie  in 
gratifying  this  sense  as  far  as  possible  with  whatever 
endowments  they  may  possess.  I  believe  that  more 
extended  observations  like  those  upon  spiders  will 
prove  that  any  variation  of  the  male  in  the  direction 
of  greater  adornment  will,  if  not  disadvantageous  to 
the  species,  increase  the  chances  of  success  in  court- 
ship. As  such  new  points  arise  the  attitudes  and 
movements  will  be  modified  in  order  to  show  them  off 
to  the  greatest  perfection. 

Mr.  Wallace,  while  admitting  the  display  and  the 
pleasure  given  by  it  to  the  females,  considers  that  it 
by  no  means  follows  that  slight  differences  of  shape, 
pattern,  or  colour  would  lead  a  female  to  prefer  one 
male  to  another,  '  still  less  that  all  the  females  of  a 
species,  or  the  great  majority  of  them,  over  a  wide 
area  of  country,  and  for  many  successive  generations, 
prefer  exactly  the  same  modification  of  the  colour  or 
ornament.' 

If,  however,  we  consider  a  hypothetical  case  in  the 
light  of  ascertained  facts,  the  probabilities  do  not 
seem  to  favour  Mr.  Wallace's  opinion.  Let  us  sup- 


306         THE  COLOURS  OF  ANIMALS 

pose  that  the  ancestor  of.Synageles  picata  only  differed 
from  this  species  in  having  the  first  pair  of  legs 
coloured  like  the  others.  The  whole  body  of  facts 
brought  together  by  G.  W.  and  E.  G.  Peckham 
strongly  support  the  opinion  that  any  variation  of  the 
male  with  rather  more  brilliant  first  legs  would  be 
preferred  by  the  great  majority  of  females,  and  that 
the  character  and  its  display  would  be  improved 
during  successive  generations  by  their  continued 
preference. 

The  courtship  of  the  Argus  Pheasant 

Mr.  Wallace  says  that  it  was  the  case  of  the 
Argus  Pheasant,  '  as  fully  discussed  by  Mr.  Darwin, 
which  first  shook  my  belief  in  "  sexual "  or  more  pro- 
perly "  female  "  selection.' ! 

Since  Darwin's  description  and  Wallace's  objection, 
Mr.  Forbes  has  given  us  an  account  of  the  habits  of 
this  bird  in  its  native  country  ;  and  the  elaborate  dis- 
play of  the  plumage  by  the  males  and  the  evident  atten- 
tion of  the  females,  render  it  at  least  probable  that 
the  latter  have  decided  opinions  as  to  the  relative 
beauty  of  their  suitors,  and  that  their  preferences 
have  led  to  the  gradual  evolution  of  the  wonderful 
markings,  shaded  so  as  to  represent '  balls  lying  loosely 
within  sockets.' 2 

Mr.  Forbes  tells  us  that  the  bird  makes  '  a  large 

1  Tropical  Nature,  pp.  205-206. 

f  The  Duke  of  Argyll  in  The  Reign  of  Law,  1867,  p.  203. 


COLOURS  PRODUCED  BY   COURTSHIP  307 

circus,  some  ten  to  twelve  feet  in  diameter,  in  the 
forest,  which  it  clears  of  every  leaf  and  twig  and 
branch,  till  the  ground  is  perfectly  swept  and  gar- 
nished. On  the  margin  of  this  circus  there  is  invari- 
ably a  projecting  branch  or  high- arched  root,  at  a 
few  feet  elevation  above  the  ground,  on  which  the 
female  bird  takes  its  place,  while  in  the  ring  the  male 
— the  male  birds  alone  possess  great  decoration — 
shows  off  all  his  magnificence  for  the  gratification  and 
pleasure  of  his  consort,  and  to  exalt  himself  in  her 
eyes.  When  the  male  bird  has  been  caught  ...  the 
female  invariably  returns  to  the  same  circus  with  a 
new  mate,  even  if  two  or  three  times  in  succession  her 
lord  should  be  caught.' ' 

Although  the  head  of  the  male  is  completely 
shielded  by  the  immense  fan-like  expansion  which  he 
unfurls  before  the  female,  he  can  judge  of  the  impres- 
sion he  is  making  by  pushing  his  head  between  two  of 
the  feathers,  or  by  peeping  round  the  edge  of  the  fan.2 


The  complete  subordination  of  Sexual  to  Natural 
Selection 

Every  one  will  admit  that  such  a  process  as  this  has 
been  rigorously  checked  by  the  far  more  important 
process  of  Natural  Selection.  But  it  does  not  there- 

1  H.  O.  Forbes,  A  Naturalist's  Wanderings  in  the  Eastern  Archi- 
pelago, p.  131. 

2  Darwin,  The  Descent  of  Man,  1874,  p.  398,  et  seq. 


308         THE  COLOUKS  OF  ANIMALS 

fore  follow,  as  Mr.  Wallace  argues,  that  '  the  effect  of 
female  preference  will  be  neutralised  by  Natural  Selec- 
tion.' It  must  be  remembered  that  such  preferences 
can  only  decide  between  males  which  have  already 
successfully  run  the  gauntlet  of  by  far  the  greatest 
dangers  which  beset  the  higher  animals,  the  dangers  of 
youth.  Natural  Selection  has  already  pronounced  a 
satisfactory  verdict  upon  the  vast  majority  of  animals 
which  have  reached  maturity.  The  male  which  has 
only  just  passed  this  test,  and  is  nevertheless  accepted 
because  of  some  superior  attraction,  will  soon  succumb 
and  will  leave  far  less  offspring  than  one  of  equal 
or  perhaps  inferior  attractions,  which  is  fitted  to  live 
for  the  natural  term  of  its  life.  Furthermore,  the 
offspring  of  the  former  will  stand  a  greater  chance  of 
failure  than  those  of  the  latter.  Natural  Selection  is  a 
qualifying  examination  which  must  be  passed  by  all 
candidates  for  honours  :  Sexual  Selection  is  an  honours 
examination,  in  which  many  who  have  passed  the  pre- 
vious examination  will  be  rejected.  But  the  conditions 
for  qualifying  are  more  rigid  than  in  any  existing 
system ;  for  the  candidates  who  have  barely  qualified, 
or  have  qualified  by  some  piece  of  luck,  or  have  failed 
to  keep  up  to  the  necessary  standard  in  after  life, 
will  in  the  end  be  excluded  from  the  advantages  of  any 
honours  they  may  have  gained. 

Mr.  Wallace  states  that  '  the  action  of  Natural 
Selection  does  not  indeed  disprove  the  existence 
of  female  selection  of  ornament  as  ornament,  but 


COLOURS  PRODUCED  BY  COURTSHIP     309 

it  renders  it  entirely  ineffective.'  This  opinion  can 
hardly  be  maintained  if  we  believe  that  such  pre- 
ference leads  to  the  failure,  comparative  or  complete, 
of  the  plainer  or  less  graceful  males,  although  the  equal 
in  other  respects  of  their  more  successful  rivals. 
Each  of  these  two  processes  will  check  the  other: 
Natural  Selection  will  ensure  that  the  males  which 
succeed  because  of  their  beauty  are  among  the  fittest ; 
Sexual  Selection  will  ensure  that  the  males  which  suc- 
ceed on  account  of  their  '  fitness  '  are  among  the 
most  beautiful. 


When  courtship  is  decided  by  wager  of  battle,  Sexual 
Selection  is  hardly  called  into  play 

When  the  males  habitually  fight  for  the  possession 
of  the  females,  and  successful  courtship  is  determined 
by  victory,  the  results  are,  as  Mr.  Wallace  points  out, 
due  to  Natural  Selection  rather  than  Sexual  Selection. 
It  is,  I  think,  in  favour  of  Mr.  Darwin's  theory,  that  any 
remarkable  beauty  of  colour  or  pattern  is  generally 
absent  when  the  possession  of  the  female  is  determined 
by  wager  of  battle ;  while  the  special  weapons  of  such 
warfare  are  generally  wanting  when  any  peculiar  beauty 
exists :  there  are,  however,  exceptions  to  this  rule.  Mr. 
Wallace  points  out  that  '  almost  all  male  animals  fight 
together,  though  not  specially  armed,'  but  there  is  no 
evidence  to  show  that  courtship  is  frequently  decided 
in  this  way. 


310          THE  COLOURS  OF  ANIMALS 

Battles  between  males  are  often  quite  unimportant 

Referring  again  to  the  spiders  of  the  family  A  ttidce, 
we  read,  in  the  paper  quoted  on  p.  297,  that  battles  be- 
tween the  males  were  extremely  common  in  the  breeding 
season,  but  nothing  seemed  to  come  of  them,  and  they 
appeared  to  be  supremely  unimportant  in  determining 
the  issue  of  courtship.  Two  males  of  Zygoballus 
bettini,  'that  were  displaying  before  one  female,  rushed 
savagely  upon  each  other  and  fought  for  twenty-two 
minutes,  during  one  round  remaining  clinched  for 
six  minutes.  .  .  .  The  combatants  appeared  tired 
at  the  close  of  the  battle,  but  after  a  short  rest  were 
perfectly  well,  and  fought  a  number  of  times  subse- 
quently.' Eight  or  ten  males  of  the  very  quarrelsome 
Dendryphantes  capitatus  were  put  in  a  box  :  «  after  two 
weeks  of  hard  fighting  we  were  unable  to  discover  one 
wounded  warrior.'  The  weaker  males  are  probably 
often  driven  away,  but  the  crucial  point  in  courtship 
is  to  win  the  consent  of  the  female,  and  this  seems  to 
have  been  obtained  by  the  tactics  already  described. 

Mr.  Wallace  refers  to  the  battles  of  butterflies,  but 
such  struggles  are  neither  common  enough  nor  fatal 
enough  to  be  of  great  importance  in  courtship.  I  have 
never  seen  any  indication  of  a  struggle  between '  assem- 
bling '  males,  and  the  courtship  of  butterflies  is  gene- 
rally allowed  to  proceed  unmolested  in  the  presence 
of  other  males,  although  interference  leading  to  a 
mild  kind  of  struggle  is  by  no  means  uncommon. 


COLOURS  PRODUCED  BY  COURTSHIP  311 


The  colours  displayed  in  courtship  are  generally  concealed 
at  other  times 

The  ceaseless  sway  of  Natural  Selection  over  all 
the  results  of  female  choice  is  well  seen  in  the  arrange- 
ments by  which  any  conspicuous  adornment  is  con- 
cealed until  it  is  wanted.  The  brilliant  legs  of  the 
male  Synageles  were  only  observed  when  they  were 
being  specially  displayed :  the  bright  colours  of  the 
upper  sides  of  the  wings  of  most  butterflies  are  con- 
cealed by  the  sombre  and  protective  tints  of  the  under 
sides,  except  during  flight  and  the  short  pauses  between 
the  flights :  the  bright  under  wings  of  many  moths 
are  similarly  concealed  by  the  upper  wings,  which  har- 
monise with  the  surroundings. 


The  colours  displayed  in  courtship  are  specially  developed 
and  specially  conspicuous  in  species  which  are  best 
adapted  to  their  conditions 

An  interesting  contrast  is  afforded  by  species  which 
are  so  perfectly  adapted  to  their  conditions  that  free 
play  is  given  to  Sexual  Selection :  in  these,  the  colours 
or  appendages  used  in  courtship  make  up  the  chief 
part  of  the  male's  appearance.  Mr.  Wallace  points  to 
the  abundance  of  birds  of  paradise  in  New  Guinea, 
and  of  peafowls  in  India,  as  proofs  that  these  species 
are  especially  well  equipped  in  the  battle  of  life,  and 


312  THE  COLOUES  OF  ANIMALS 

he  believes  that  scope  has  thus  been  given  to  the  causes 
which  have  produced  the  sexual  adornment.  This 
argument  of  course  holds  good,  even  if  we  are  com- 
pelled to  reject  the  causes  suggested  by  him.  A  still 
better  example  is  afforded  by  the  Australian  pigeons, 
which  '  are  sometimes  adorned  with  colours  vying 
with  those  of  the  gayest  parrots  and  chatterers.'  Mr. 
Wallace  explains  this  fact  as  due  to '  the  entire  absence 
of  monkeys,  cats,  lemurs,  weasels,  civets,  and  other 
arboreal  mammals ' ;  while  the  green  colour  of  the 
upper  part  may  be  due  to  the  need  of  concealment 
from  birds  of  prey.  In  some  small  islands  of  the 
Pacific,  where  such  foes  are  very  scarce,  the  pigeons 
may  assume  a  rich  yellow  colour.1  We  see  the  same 
tendency  in  those  predaceous  insects  which  have  little 
to  fear,  and  which  are  swift  enough  to  catch  their 
prey  without  attempt  at  concealment. 

The  dangers  of  bright  sexual  colouring  may  be  averted 
by  extreme  wariness 

In  many  cases  the  danger  incurred  by  the  attain- 
ment of  sexual  colours  may  be  balanced  by  the  special 
development  of  some  quality  such  as  extreme  wariness. 
I  was  very  much  struck  by  the  opposite  kinds  of 
colouring  exhibited  by  the  fish  which  were  extremely 
abundant  at  low  water  in  the  rock  pools  at  Orotava, 
Teneriffe.  The  colours  of  some  were  extremely  beauti- 

1  Wallace,  Distribution  of  Animals,  vol.  i.  p.  395. 


COLOURS  PRODUCED  BY  COURTSHIP  .    313 

ful  and  bright,  but  those  were  always  very  shy  and 
difficult  to  catch ;  others  were  protectively  coloured 
and  exactly  resembled  the  sand,  rock,  or  sea- weed,  and 
these  when  detected  were  easily  captured.  Professor 
W.  A.  Herdman  of  Liverpool  has  also  observed  the 
same  facts  in  other  groups  of  marine  animals. 


314         THE  COLOURS  OF  ANIMALS 


CHAPTEE  XVI 

OTHER   THEORIES  OF  SEXUAL   COLOURING 

IT  now  remains  to  consider  the  causes  which  Mr. 
Wallace  and  other  writers  believe  to  have  been  efficient 
in  producing  sexual  colouring. 

A  wide  extension  of  the  principle  of  Recognition  Mark- 
ings is  believed  largely  to  explain  sexual  colouring 

In  the  first  place,  this  distinguished  naturalist 
very  widely  extends  the  principle  of  Kecognition  Mark- 
ings, and  believes  that  one  of  the  chief  meanings  of 
sexual  colouring  is  to  enable  '  the  sexes  to  recognise 
their  kind,  and  thus  avoid  the  evils  of  infertile  crosses.' 
Thus  he  considers  that  '  among  insects  the  principle 
of  distinctive  colouration  for  recognition  has  probably 
been  at  work  in  the  production  of  the  wonderful  diver- 
sity of  colour  and  marking  we  find  everywhere,  more 
especially  among  the  butterflies  and  moths;  and  here 
its  chief  function  may  have  been  to  secure  the  pairing 
together  of  individuals  of  the  same  species.' 


OTHER  THEORIES  OF  SEXUAL  COLOURING   315 

Recognition  between  the  sexes  appears  to  be  complete, 
and  infertile  crossing  does  not  occur  even  when 
two  species  closely  resemble  each  other 

To  this  it  may  be  replied  that  pairing  between  the 
individuals  of  distinct  species  is  extremely  rare,  and 
does  not  seem  to  be  any  commoner  among  species  in 
which  this  means  of  recognition  would  lead  to  failure. 
If  the  resemblance  between  the  white  variety  of  the 
female  Clouded  Yellow  (Colias  edasa,  var.  helice)  and 
the  female  Pale  Clouded  Yellow  (Colias  hyale)  does  not 
lead  to  infertile  pairing ;  if  the  practical  identity  of 
the  Sallow  and  Poplar  Kittens  (Cerurafurcula  and  C. 
bifida),  of  the  Swallow  Prominent  and  Lesser  Swallow 
Prominent  (Leiocampa  dictcea  and  L.  dlctaoides) ,  of 
the  Common  and  Dark  Dagger  Moths  (Acronycta  psi 
and  A.  tridens),  does  not  lead  to  dangers  of  the  kind, 
we  must  conclude  that  wide  differences  of  colour  and 
pattern  cannot  have  been  produced  by  a  gradually 
lessening  number  of  infertile  crosses. 

In  the  case  of  mimetic  species,  it  is  a  comparatively 
common  thing  for  the  female  of  one  species  to  be 
chased  by  the  male  of  another,  and  yet,  in  spite  of  a 
wonderful  superficial  resemblance  between  the  females, 
it  is  very  improbable  that  the  courtship  proceeds 
beyond  its  most  preliminary  stages.  The  same  is  true 
of  the  Clouded  Yellows  referred  to  above,  and  of 
Clouded  Yellows  and  Common  Whites,  These,  and 
many  other  examples  of  the  kind  show  that  this  means 


316  THE  COLOUES  OF  ANIMALS 

of  sexual  recognition  may,  and  frequently  does,  fail 
without  injury  to  the  species. 

One  of  the  most  fundamental  instincts  provides 
for  an  unfailing  recognition  between  the  sexes,  in 
which  certainty  is  ensured  by  the  unanimous  witness 
of  all  the  senses,  so  that  even  the  closest  resemblance 
between  distinct  species  does  not  appear  to  produce 
any  evils  of  the  kind  suggested  by  Mr.  Wallace. 


The  necessity  for  Recognition  can  never  explain  the 
aesthetic  value  of  the  results  produced 

It  may  also  be  urged  that  the  beauty  of  the  colours 
and  patterns  displayed  in  courtship  can  never  be 
explained  by  this  principle.  For  the  purposes  of  recog- 
nition, beauty  is  entirely  superfluous  and  indeed  un- 
desirable ;  strongly  marked  and  conspicuous  differences 
are  alone  necessary.  But  these,  which  are  so  well 
marked  in  Warning  Colours,  are  not  by  any  means 
characteristic  of  those  displayed  in  courtship. 

If  an  artist,  entirely  ignorant  of  natural  history, 
were  asked  to  arrange  all  the  brightly  coloured  butter- 
flies and  moths  in  England  in  two  divisions,  the  one 
containing  all  the  beautiful  patterns  and  combinations 
of  colour,  the  other  including  the  staring,  strongly 
contrasted  colours,  and  crude  patterns,  we  should  find 
that  the  latter  would  contain,  with  hardly  an  exception, 
the  species  in  which  independent  evidence  has  shown, 
or  is  likely  to  show,  the  existence  of  some  unpleasant 


OTHER  THEORIES  OF  SEXUAL  COLOURING      317 

quality.  The  former  division  would  contain  the 
colours  displayed  in  courtship  and  when  the  insect  is 
on  the  alert,  concealed  at  other  times. 

The  immense  difference  between  the  two  divisions, 
the  one  most  pleasing,  the  other  highly  repugnant  to 
our  sasthetic  susceptibilities,  seems  to  me  to  be  entirely 
unexplained  if  we  assume  that  the  colours  of  both  are 
intended  for  the  purposes  of  recognition.  But  these 
great  differences  are  to  be  expected  if  we  accept  Mr. 
Darwin's  views  ;  for  the  colours  and  patterns  of  the 
latter  division  appeal  to  a  vertebrate  enemy's  sense  of 
what  is  conspicuous,  while  those  of  the  former  appeal 
to  an  insect's  sense  of  what  is  beautiful.  It  is,  of 
course,  highly  remarkable  that  our  own  aesthetic  sense 
should  so  closely  correspond  with  that  of  an  insect. 
I  believe,  however,  that  it  is  possible  to  account  for 
this  wonderful  unanimity  in  taste. 


Our  standards  of  beauty  have  been  largely  created  for  us 
by  insects 

Our  standards  of  beauty  are  largely  derived  from 
the  contemplation  of  the  numerous  examples  around 
us,  which,  strange  as  it  may  seem,  have  been  created 
by  the  aesthetic  preferences  of  the  insect  world.  One 
of  the  most  fruitful  inquiries  originated  by  Darwin 
has  been  the  renewed  investigation  of  the  marvellous 
relation  between  insects  and  flowers,  a  subject  which 

had  been  previously  attacked  by  Sprengel  in  1798. 
15 


318         THE  COLOURS  OF  ANIMALS 

Darwin's  work  has  been  extended  by  others,  and 
especially  by  Hermann  Miiller.  As  the  result  of  these 
investigations  it  is  now  well  known  that  the  fertilisa- 
tion of  flowers  has  been  largely  carried  on  by. insect 
agency,  and  that  insect  preferences  have  decided  as 
to  the  colours  and  patterns  which  prevail  among  the 
wild  flowers  of  any  country.1  This  is  now  generally 
admitted,  and  as  Mr.  Wallace  himself  points  out,  '  we 
have  abundant  evidence  that  whenever  insect  agency 
becomes  comparatively  ineffective,  the  colours  of  the 
flowers  become  less  bright,  their  size  and  beauty 
diminish,  till  they  are  reduced  to  such  small,  greenish, 
inconspicuous  flowers  as  those  of  the  rupture-wort 
(Herniaria  glabra) ,2 ' 

But  if  this  conclusion  be  accepted,  if  the  beauty 
of  flowers  has  followed  so  completely  from  insect 
selection,  are  we  not  compelled  to  admit  that  insects 
possess  an  aesthetic  sense — a  sense  which  could  dis- 
criminate between  the  slightly  different  attractions 
displayed  by  suitors,  just  as  we  all  admit  that  it  has 
discriminated  between  the  slightly  different  attractions 
displayed  by  flowers  ? 


1  Consult   The  Fertilisation  of  Flowers,  by  Hermann  Miiller, 
English  translation  by  D'Arcy  W.  Thompson :  London.    Also  British 
Wild  Flowers  in  relation  to  Insects,  by  Sir  John  Lubbock :  Nature 
Series. 

2  Z/oc.  cit.  p.  332. 


OTHER  THEORIES  OF  SEXUAL  COLOURING      319 


The  musical  value  of  the  song  of  birds  cannot  be  explained 
as  a  means  of  Recognition  between  the  sexes 

Similar  objections  may  be  urged  against  Mr. 
Wallace's  contention  that  the  songs  of  birds  are  to 
be  explained  as  a  means  of  recognition,  and  that  their 
*  production,  intensification,  and  differentiation  are 
clearly  within  the  power  of  natural  selection.'  Eecog- 
nition  between  the  sexes,  and  invitation  from  the  male 
to  the  female,  are  most  important  benefits  conferred 
by  song,  but  these  can  never  account  for  the  marvel- 
lous degree  of  elaboration,  and  the  high  musical  value 
of  the  results  attained  by  many  of  our  singing  birds. 
The  beauty  of  song  is  something  more  than  its  '  clear- 
ness, loudness,  and  individuality,'  just  as  the  beauty 
of  appearance  is  something  more  than  its  conspicuous- 
ness  ;  and  the  fact  that  these  two  forms  of  beauty  are 
complementary,  so  that  the  brightest  birds  do  not  sing, 
while  song  birds  are  sober  in  appearance,  is  quite 
consistent  with  the  origin  of  these  qualities  by  the 
accumulated  results  of  female  preference.  We  know 
that  the  excessive  cultivation  of  one  taste  is  inconsis- 
tent with  the  equal  cultivation  of  others,  and  when 
the  small  brain  of  a  bird  is  constantly  directed  to 
appreciating  the  beauty  of  song,  it  may  well  become 
comparatively  indifferent  to  beauty  of  person.  Be- 
sides, the  qualities  conferred  by  this  means  are  always 
more  or  less  of  a  danger  to  the  species,  and  an  especi- 


320         THE  COLOUES  OF  ANIMALS 

ally  high  development  in  one  direction  will  tend  to 
prevent  any  great  development  in  other  directions. 

The  habits  of  Bower-birds  as  evidence  for  the  existence 
of  an  aesthetic  sense 

The  habits  of  the  Australian  Bower-birds  are  fur- 
ther evidence  for  the  existence  of  a  strongly  marked 
aesthetic  sense  in  birds.  Just  as  certain  females  are 
gratified  by  the  display  of  personal  adornment  on  the 
part  of  their  suitors,  others  are  pleased  by  the  display 
and  arrangement  of  beautiful  or  curious  objects  col- 
lected in  the  bowers.  The  latter  are  built  on  the 
ground  and  are  intended  for  courtship  alone,  the 
nests  being  formed  in  trees.  They  are  often  very 
elaborate  structures,  and  each  species  decorates  its 
bower  in  a  different  manner.  The  Satin  Bower-bird 
collects  brightly  coloured  feathers,  bleached  bones, 
and  shells :  '  these  objects  are  continually  rearranged, 
and  carried  about  by  the  birds  whilst  at  play.'  The 
Spotted  Bower-bird  lines  its  bower  with  tall  grasses, 
kept  in  place  by  round  stones  which  are  brought  from 
great  distances,  together  with  shells.  The  Eegent 
bird  makes  use  of  bleached  shells,  blue,  red,  and 
black  berries,  fresh  leaves,  and  pink  shoots ;  '  the 
whole  showing  a  decided  taste  for  the  beautiful.' ' 

I  have  mentioned  these  well-known  but  most  inte- 
resting facts,  which  were  considered  by  Darwin  as 

1  The  facts  are  quoted  by  Darwin  from  Gould  and  Ramsay, 
Descent  of  Man,  pp.  413,  414. 


OTHEE  THEORIES  OF  SEXUAL  COLOURING      321 

'the  best  evidence  ...  of  a  taste  for  the  beautiful,' 
because  of  the  confirmation  which  has  been  afforded 
by  some  more  recent  observations  upon  a  New  Guinea 
Bower -bird. 

All  the  aesthetic  taste  of  this  bird  appears  to  be 
concentrated  on  the  bower  and  its  surroundings,  for 
the  bird  itself  is,  as  its  name  (Amblyornis  inornata) 
implies,  very  plainly  coloured.  It  is  called  the 
Gardener  Bower-bird,  because  of  its  remarkable 
habits,  and  its  native  name  also  means  '  the  gardener.' 
The  bower  and  adjacent  '  small  meadow  enamelled 
with  flowers '  were  seen  by  the  Italian  traveller,  Dr. 
Beccari,1  on  Mount  Arfak,  in  New  Guinea.  He  states 
that  the  Amblyornis  chooses  a  flat  surface  at  the  base 
of  a  small  tree,  against  which,  as  a  central  pillar,  it 
builds  a  very  regular  conical  hut,  with  an  opening  at 
one  point.  The  hut,  which  is  nearly  three  feet  in 
diameter  at  the  base,  is  formed  of  the  twigs  of  an 
orchid,  which,  being  an  epiphyte,  bears  fresh  leaves 
for  a  very  long  time,  and  greatly  adds  to  the  beauty  of 
the  bower.  Within  the  hut  a  small  cone  of  moss,  about 
the  size  of  one's  hand,  is  heaped  round  the  base  of 
the  tree.  'Before  the  cottage  there  is  a  meadow, of 
moss.  This  is  brought  to  the  spot  and  kept  free 
from  grass,  stones,  or  anything  which  would  offend 

1  An  abstract  of  Dr.  Beccari's  description  appeared  in  The  Gar- 
deners' Chronicle,  March  16,  1878,  with  a  figure  of  the  bower  re- 
produced from  a  painting  made  on  the  spot.  This  article  is  quoted 
in  Gould's  Birds  of  New  Guinea,  vol.  i.,  which  also  contains  a 
coloured  plate  founded  upon  the  above-mentioned  figure. 


322         THE  COLOUKS  OF  ANIMALS 

the  eye.  On  this  green  turf  flowers  and  fruit  of 
pretty  colour  are  placed,  so  as  to  form  an  elegant 
little  garden.  The  greater  part  of  the  decoration  is 
collected  round  the  entrance  to  the  nest,  and  it  would 
appear  that  the  husband  offers  there  his  daily  gifts  to 
his  wife.'  Among  the  objects — which  were  always 
brightly  coloured — Dr.  Beccari  noticed  the  fruit  of 
Garcinia,  like  small  apples ;  the  fruits  of  Gardenias ; 
the  '  beautiful  rosy  flowers  of  a  splendid  new  V actinium 
(Agapetes  amblyornitliis) ; '  fungi,  and  mottled  insects. 
'  As  soon  as  the  objects  are  faded  they  are  moved  to 
the  back  of  the  hut/  It  is  not  known  whether  the  • 
female  assists  the  male  in  making  the  bower,  which 
is  believed  to  last  several  seasons. 

I  think  it  may  be  safely  affirmed  that  the  expla- 
nation of  sexual  colours  as  a  means  of  recognition  can 
never  account  for  their  aesthetic  value,  while  the  ex- 
istence of  an  aesthetic  sense,  to  which  such  characters 
may  appeal,  appears  to  be  rendered  certain  by  many 
observations. 


The  hypothesis  that  sexual  colouring  is  due  to  a  surplus 
of  vitality  or  is  developed  in  relation  to  underlying 
structures 

Mr.  Wallace  also  believes  that  the  appearance  of 
beautiful  colours  and  the  growth  of  plumes  and  other 


OTHER  THEOEIES  OF  SEXUAL  COLOURING      323 

appendages  is  due  to  a  surplus  of  vitality,  and  may  be 
connected  with  the  vivacity  and  excitability  of  the 
males  in  the  breeding  season.  He  also  accepts  Mr. 
Alfred  Tylor's  theory  that  colours  and  patterns  are 
developed  in  relation  to  underlying  organs  and  struc- 
tures. It  is  convenient  to  discuss  these  two  views 
together,  for  they  have  much  in  common. 

Mr.  Tylor  argued  that  the  modification  of  pattern 
in  the  different  regions  of  the  body  of  such  an  animal 
as  the  zebra,  is  related  to  the  changes  in  the  various 
parts  of  the  skeleton  which  are  concealed  beneath  the 
surface ;  he  even  believed  that  the  black  marks  on  the 
heads  of  tigers,  &c.,  are  related  to  the  chief  convolu- 
tions on  the  surface  of  the  brain  beneath. 

It  is  quite  possible  to  understand  why  the  pattern 
should  change  in  the  different  regions  of  the  animal 
body,  because  of  the  greater  protective  value  or  higher 
aesthetic  effect  of  such  an  arrangement,  so  that  if 
Sexual  Selection  be  accepted  Mr.  Tylor's  theory  be- 
comes unnecessary.  Furthermore,  it  is  difficult  to  see 
why  such  an  inert,  although  important,  structure  as 
the  skeleton  should  so  greatly  affect  the  appearance  of 
an  animal.  Why  should  not  the  liver,  with  its  vast 
blood-supply  and  manifold  functions,  produce  some 
of  the  effects  believed  to  be  wrought  by  one  of  the 
most  passive  tissues  in  the  body  ?  Or  if  the  muscles 
and  nerves  which  follow  the  skeleton  are  supposed  to 
be  the  efficient  cause,  rather  than  the  bones  them- 
selves, it  must  be  pointed  out  that  the  structure  of 


324  THE  COLOURS  OF  ANIMALS 

such  nerve-  and  muscle-fibres,  together  with  the  im- 
pulses which  pass  along  the  one  and  the  contractions 
which  are  evoked  in  the  other,  are  essentially  similar 
throughout. 

The  colours  of  underlying  structures  may  be  made 
use  of  in  many  cases 

It  is  perfectly  true  that  the  colours  of  underlying 
structures  may  be  made  use  of  for  ornamental  or  pro- 
tective purposes.  The  red  colour  of  our  blood  is 
useless  as  colour  in  most  parts  of  the  body,  but  the 
transparency  of  the  skin  has  permitted  it  to  be  made 
use  of  in  the  acquisition  of  'complexion';  and  I 
believe  that  I  am  not  wrong  in  supposing  that  we  are 
still  true  to  the  preference  which  has  doubtless  en- 
couraged the  growth  of  this  attraction. 

The  same  thing  is  true  of  many  insects  in  which 
the  white  colour  of  fat,  the  green  colour  of  the  blood,  or 
even  of  the  food  lying  in  the  alimentary  canal,  may  be 
employed  in  the  production  of  a  protective  appearance 
(see  p.  89,  also  pp.  79,  80).  Natural  Selection  has  ren- 
dered these  ready-made  colours  available  by  making 
the  superficial  parts  transparent,  and  in  many  cases 
such  stint  have  been  deepened  or  outlines  strengthened 
by  the  appearance  of  true  pigment  in  the  skin.  But 
these  admitted  facts  do  not  support  the  theory  that  there 
is  any  necessary  relationship  between  superficial  pig- 
ment and  the  organs  or  structures  which  lie  beneath. 


OTHEE  THEORIES  OF  SEXUAL  COLOURING       325 


The  objection  to  Mr.  Wallace's  explanation  of  the 
immense  tufts  on  Birds  of  Paradise 

Mr.  Wallace,  however,  follows  up  this  idea,  and 
argues  that  '  the  immense  tuft  of  golden  plumage  in 
the  best  known  birds  of  paradise '  is  related  to  the 
proximity  of  the  most  powerful  muscle  in  the  body 
(the  pectoral),  of  certain  large  blood-vessels  and 
nerves,  and  of  certain  parts  of  the  skeleton.  The 
contractions  of  the  muscle  mean  of  course  a  great 
expenditure  of  energy,  but  the  present  state  of  phy- 
siology lends  no  support  to  the  opinion  that  such 
expenditure  could  afford  any  explanation  of  the  size  and 
special  peculiarities  of  an  appendage  produced  by  an 
adjacent  surface.  The  nervous  and  arterial  trunks 
imply  that  nervous  energy  and  food  material  are 
being  conveyed  in  large  quantities  to  the  localities 
where  the  nerves  and  arteries  are  finally  distributed  ; 
but  their  size  and  importance  as  they  pass  beneath 
the  base  of  the  tuft  can  have  no  relation  to  the  growth 
and  appearance  of  the  latter.  The  travelling  facilities 
and  means  of  communication  in  any  village  depend 
upon  the  local  arrangements  of  its  railway  station  and 
telegraph  office ;  not  upon  the  number  of  express- 
trains  and  telegrams  which  rush  through  it  on  their 
way  to  a  distant  town. 


326         THE  COLOURS  OF  ANIMALS 


The  supposed  causes  of  colouring  suggested  by  Wallace 
and  Tylor  bear  no  true  relation  to  the  effects 

But  even  greater  difficulties  are  encountered  by 
those  who  accept  Mr.  Wallace's  and  Mr.  Tylor's  views 
upon  the  subject.  If  colours  and  patterns  were  in- 
variably caused  by  different  kinds  of  colouring  matter 
or  pigment,  it  might  not  appear  to  be  very  improbable 
that  the  kind  of  pigment,  and  therefore  the  kind  of 
colour,  might  be  slightly  varied  as  a  result  of  the 
causes  suggested  by  these  writers:  but  even  then 
there  would  not  be  any  foundation  for  the  assumption 
that  the  pigments  which  produce  the  brightest  colours 
are  necessarily  more  difficult  of  elaboration  than  the 
others,  or  more  likely  to  be  formed  by  an  organism 
with  surplus  vitality  or  upon  that  portion  of  the  sur- 
face beneath  which  the  most  important  functions  are 
performed.  A  change  of  chemical  composition  will 
nearly  always  mean  the  absorption  of  different  rays  of 
light  and  therefore  a  different  colour ;  but  the  quality 
of  the  latter,  as  measured  by  our  sesthetic  sense,  will 
bear  no  necessary  relation  to  the  strain  put  upon  the 
organism  in  producing  the  pigment. 

When,  however,  we  remember  that  a  very  large 
proportion  of  the  colours  and  patterns  distinctive  of 
Bex  are  only  partially  dependent  upon  pigment,  the 
difficulties  become  insuperable.  Let  us  first  consider 
the  case  of  white,  which  forms  an  important  part  in 


OTHER  THEORIES  OF  SEXUAL  COLOURING      327 

the  patterns  of  so  many  birds  and  mammals.  The 
whiteness  of  a  hair  or  feather  is  produced,  just  as  the 
whiteness  of  snow  is  produced,  by  the  presence  of  gas 
entangled  in  the  loose  meshes  between  the  component 
parts  of  their  substance  (see  pp.  3-6).  We  cannot 
suppose  that  the  surplus  vitality  which  is  believed  to 
be  efficient  in  producing  some  new  or  especially  bright 
colouring  matter  on  one  part,  will  on  another  part  be 
equally  efficient  in  withholding  it !  and  in  causing  the 
substitution  of  bubbles  of  gas. 

But  white  is  not  the  only  difficulty;  the  most 
beautiful  of  all  colours  in  nature,  the  iridescent  tints 
of  many  animals,  are  not  due  to  pigment  at  all,  but 
frequently  to  interference  of  light,  the  cause  which 
produces  the  colours  of  a  soap-bubble  or  that  of 
mother-of-pearl  (see  pp.  6-10). 

The  interference  colours  of  animals  are  similarly 
due  to  fine  lines  on  the  surface  of  structures,  or  more 
frequently  to  excessively  thin  sheets  of  air  or  occa- 
sionally of  fluid,  enclosed  between  layers  of  denser 
substance.  The  varying  tints  are  caused  by  excessively 
minute  differences  in  the  width  of  the  chinks  in  which 
the  air  is  contained.  But  it  would  be  a  very  rash 
hypothesis  which  suggests  that  a  surplus  of  vitality 
regulates  the  width  of  these  chinks  to  the  production 
of  this  or  that  colour.  There  is  absolutely  no  reason 

1  When  a  permanent  white  patch  appears  upon  a  mammal,  the 
pigment  is  withheld ;  it  is  only  retained,  and  masked  by  the  forma- 
tion of  gas-bubbles,  in  the  whitening  of  existing  dark  hairs  (sea 
pp.  98,  99). 


328         THE  COLOURS  OF  ANIMALS 

for  believing  that  a  width  which  just  prevents  the 
appearance  of  colour  is  an  indication  of  want  of 
vitality. 

We  must  also  remember  that  these  iridescent 
tints  occur  in  combination  with  colours  produced  in 
other  ways.  If  we  take  a  hypothetical  case,  the 
inadequacy  of  '  surplus  vitality '  as  an  explanation 
becomes  at  once  apparent. 

Let  us  suppose  that  a  male  bird  becomes  more 
beautiful  in  appearance,  and  that  the  change  consists 
in  the  addition  of  white  feathers,  of  new  tints  or 
shades  in  the  colours  due  to  pigments,  and  of  those 
due  to  interference.1  We  must  therefore  suppose  that 
a  '  surplus  of  vitality '  favours  the  disappearance  of 
pigment  and  the  substitution  of  bubbles  of  gas,  in 
one  part,  although  albinism  affords  rather  strong 
evidence  that  such  a  result  is  certainly  not  an  indica- 
tion of  strength  :  we  must  suppose  that  the  same 
cause  favours  slight  changes  in  the  chemical  con- 
stitution of  pigments,  in  other  parts,  involving  the 
excessively  unlikely  hypothesis  that  the  aesthetic 
value  of  the  results  is  a  measure  of  the  difficulty 
involved  in  their  production :  and  we  must  finally 
suppose  that,  elsewhere,  the  same  cause  is  efficient 
in  adjusting  with  mathematical  precision  the  width 
of  spaces  in  the  tissue,  although  it  is  wildly  im- 
probable that  the  minute  differences  which  correspond 

1  Admitting,  for  the  sake  of  argument,  that  this  cause  is  effective 
in  birds,  as  it  certainly  is  in  insects. 


OTHER  THEORIES  OF  SEXUAL  COLOURING      329 

to  the  production  or  change  of  colour  bear  such  a 
relation  to  the  vital  energy  expended  in  their  develop- 
ment, that  we  can  judge  of  the  amount  of  the 
expenditure  by  the  degree  of  admiration  excited  in 
ourselves.1 


The  effects  are  only  explicable  by  a  theory  of 
selective  breeding 

We  are  also  required  to  believe  that  these  hetero- 
geneous elements  are  combined  by  the  same  means 
into  an  elaborate  and  harmonious  whole.  A  process 
of  selective  breeding,  like  that  of  Sexual  Selection, 

1  A  white  peacock  in  the  Zoological  Gardens,  shown  to  me  by  Mr. 
F.  E.  Beddard,  appears  at  first  sight  to  support  Mr.  Wallace's  views  ; 
for  the  '  pigment '  colours  and  '  structural '  colours  are  alike  absent 
(see  p.  11).  Closer  examination  reveals  the  fact  that  regions  in 
which  '  structural '  colours  usually  appear  are  readily  recognisable, 
the  white  being  of  a  different  quality.  The  '  eyes  '  on  the  train,  for 
example,  are  quite  distinct,  coming  out  like  the  pattern  on  a  white 
damask  table-cloth. 

Dr.  Gadow  informs  me  that  the  same  fact  is  true  of  white  ducks 
and  drakes,  the  wing  coverts,  which  are  blue  in  normally  pigmented 
individuals,  exhibiting  a  peculiar  sheen  or  gloss,  differing  from  the 
rest  of  the  plumage.  Dr.  Gadow  states  that  the  structural  colours 
are  absent,  because  the  existence  of  a  pigment  beneath  the  super- 
structure is  necessary  in  order  to  show  them  off  ;  and  he  points  out 
that  the  ancestors  of  birds  with  such  structural  colours  cannot  well 
have  been  white,  because  the  effect  depends  in  part  upon  pigment. 

Mr.  Gotch  and  I  found  that  the  '  eyes  '  of  the  white  peacock  do 
not  regain  the  normal  appearance  in  any  of  the  colours  of  the 
spectrum,  nor  when  examined  by  monochromatic  light. 

Inasmuch  as  we  can  trace  the  form  and  distribution  of  all  structural 
markings  in  an  albino  animal,  it  is  clear  that  the  physical  cause  of 
the  appearance  is  not  affected  by  albinism,  in  the  same  manner  as 
the  cause  of  pigment  colours. 


330  THE  COLOURS  OF  ANIMALS 

affords  an  explanation  of  the  gradual  growth  of  such 
a  pattern  in  spite  of  its  heterogeneous  elements,  an 
explanation  which  I  do  not  think  is  supplied  by  any 
other  theory.  Mr.  Wallace  has  greatly  insisted  on 
the  amount  of  individual  variation,  and  we  know  that 
variations  in  the  minutest  elements  of  organs  must 
occur  as  constantly  as  in  the  organs  themselves.  The 
presence  or  absence  of  bubbles  of  gas  and  of  pigment, 
the  chemical  constitution  of  pigments,  the  width  of 
spaces  in  the  tissues,  are  all  subject  to  constant  varia- 
tion, and  afford  abundant  material  for  the  production 
of  any  aesthetic  effect,  if  only  subjected  to  selective 
breeding.  And  I  have  endeavoured  to  show  that 
selection  by  female  preference  is  now  supported  by 
certain  striking  facts,  which  were  not  available  when 
Darwin  first  argued  that  this  principle  has  been  effi- 
cient in  producing  the  colours  displayed  in  courtship. 

The  unsatisfactory  nature  of  the  phrase  '  surplus  of  vital 
energy ' 

I  will  only  briefly  allude  to  the  unsatisfactory  nature 
of  such  vague  phrases  as  '  surplus  of  vital  energy,' 
when  used  to  explain  the  appearance  of  the  definite 
results  which  have  been  described  above.  The  only 
evidence  for  such  surplus  vitality  is  the  excitability  of 
the  nervous  system,  which  is  correlated  with  the  ac- 
tivity of  the  reproductive  organs  in  the  breeding  sea- 
son, and  which  leads  to  violent  and  active  movements 
generally  forming  part  of  the  display  in  courtship. 


OTHER  THEORIES  Of  SEXUAL  COLOURINO      331 


Certain  general  considerations  which  support  Darwin's 
theory  of  Sexual  Selection 

There  are  also  one  or  two  general  facts  which  seem 
to  me  to  strongly  support  the  theory  of  Sexual  Selec- 
tion, and  to  oppose  any  theory  which  is  not  based  on 
selective  breeding. 


Sexnal  Colours  only  developed  in  species  which  court 
by  day  or  twilight,  or  have  probably  done  so  at  no 
distant  date 

The  appearance  of  beautiful  colours  and  patterns, 
which  are  displayed  in  courtship,  invariably  occurs  in 
diurnal  or  partially  diurnal  animals.  The  colours 
only  appear  when  the  conditions  for  female  preference 
are  present  also.  If  we  compare  butterflies  with  moths, 
or  moths  which  fly  by  day  and  twilight  with  those 
which  fly  in  darkness,  we  find  that  brilliant  tints  and 
ornamental  patterns  are  only  found  when  there  is  light 
enough  for  the  female  to  see  them.  The  consideration 
of  apparent  exceptions  will  be  found  to  support  the 
argument.  The  same  evidence  may  be  drawn  from 
birds  and  other  animals.  If,  however,  such  colours 
were  merely  the  symptom  of  vitality,  we  should  not 
expect  to  find  this  invariable  relationship  between  the 
colours  of  one  sex  and  the  conditions  for  seeing  it  in 
the  other. 


332         THE  COLOURS  OF  ANIMALS 

Sexual  Colours  are  not  developed  on  parts  of  the  body 
which  move  so  rapidly  that  they  become  invisible 

Another  fact  of  the  same  kind  has  only  suggested 
itself  to  me  lately.  The  bright  colours  of  courtship 
are  especially  characteristic  of  two  groups  of  animals, 
birds  and  insects,  and  it  may  not  unreasonably  be  sup- 
posed that  this  fact  is  related  to  the  convenient  frame- 
work afforded  by  the  surface  of  the  wings.  In  each 
group  we  may  distinguish  two  kinds  of  flight :  in  one 
it  is  produced  by  an  excessively  swift  vibration  of  the 
wings,  in  the  other  by  a  relatively  slow  flapping  move- 
ment. In  the  former,  including  the  humming-birds 
and  the  majority  of  insects,  the  wings  are  quite 
invisible,  owing  to  their  rapid  motion ;  in  the  latter, 
including  the  majority  of  birds  and  butterflies  and 
many  moths,  they  can  be  easily  seen.  We  find,  as  a 
general  rule,  that  the  colours  distinctive  of  sex  are 
displayed  on  the  wings  in  the  latter  group,  but  are 
absent  from  the  wings  in  the  former.  Facilities  for 
female  observation  are  thus  afforded  by  the  distribu- 
tion of  colour. 

When  colours  are  best  seen  from  one  direction,  this 
corresponds  with  the  position  in  which  the  female 
would  see  them 

Again,  the  magnificent  iridescent  colours  on  the 
wings  of  certain  butterflies,  due  to  interference  of  light, 


OTHER  THEORIES  OF  SEXUAL  COLOURING      333 

are  best  seen  when  the  insect  is  looked  at  from  in  front, 
as  it  would  be  by  a  female  when  the  male  is  approaching 
her.  Mr.  Wallace,  however,  argues  that  the  malefollows 
the  female  and  hovers  over  her,  so  that  she  can  hardly 
see  the  upper  side  of  his  wings  at  all.  We  know  but 
little  of  the  way  in  which  an  insect  sees;  but  the  struc- 
ture of  the  eye  as  a  large  rounded  mass  made  up  of 
radiating  elements  renders  it  probable  that  any  object 
which  comes  within  the  area  obtained  by  prolonging 
the  radii  will  be  seen,  provided  it  is  at  the  right  dis- 
tance. Hence  the  male  would  be  seen  approaching 
the  female  from  behind,  in  front,  or  the  side,  and  the 
only  requisite  for  producing  the  best  impression  upon 
her  is  that  his  head  shall  be  towards  her,  and  that  the 
upper  side  of  the  wings  shall  be  seen.  The  courtship 
of  a  butterfly  usually  passes  through  three  stages :  in 
the  first,  the  male  sees  the  female  and  approaches 
her ;  in  the  second,  they  fly  together  for  a  variable 
distance,  fluttering  around  and  about  each  other, 
although  the  male  is  probably  the  more  active  and 
the  pursuer ;  in  the  third,  the  female  has  been  over- 
come by  the  attentions  of  the  male,  she  no  longer 
flies,  but  settles  on  the  ground  or  a  leaf,  while  the 
male  flutters  over  her  and  finally  settles  also.  In 
each  of  these  phases  the  planes  of  both  body  and 
wings  are  ever  shifting,  and  the  upper  side  of  the 
latter  is  certainly  visible  to  the  female  from  time  to 
time.  It  is  therefore  most  significant  that  the  irides- 
cent colours  of  Diadema  bolina  should  be  seen  from 


334         THE  COLOURS  OF  ANIMALS 

the  front,  while  they  become  invisible  from  the  side 
or  from  behind,  for  the  colour  is  produced  in  such  a 
way  as  to  give  the  female  the  best  chance  of  seeing  it, 
a  fact  which  is  unexplained  by  any  other  theory  of 
origin  except  that  of  Sexual  Selection.  At  the  same 
time  this  observation  needs  testing  by  further  and 
exact  observation  of  the  habits  of  many  iridescent 
species  during  courtship. 


The  evidence  for  the   gradual   development   of  pattern 
suggests  selective  breeding 

The  steps  by  which  some  of  the  most  elaborate  and 
wonderful  appearances  have  arisen,  are  traced  by  Mr. 
Darwin  in  the  most  complete  and  convincing  manner. 
When  we  look  at  the  marvellous  eyes  upon  the  train  of  a 
Peacock,  or  the  more  beautiful  markings  on  the  feathers 
of  the  male  Argus  Pheasant,  it  seems  impossible  that  so 
wonderful  and  complete  a  result  can  have  been  produced 
by  the  aesthetic  preferences  of  female  birds.  And  yet  Mr. 
Darwin  shows  the  relation  between  these  characters  and 
much  simpler  markings  on  other  parts  of  the  surface. 
He  proves  that  the  one  has  been  derived  from  the  other 
by  gradual  modification,  and  he  points  to  traces  of 
the  original  marking  which  persist  in  the  complex 
appearance  to  which  it  has  given  rise.  Such  facts, 
while  eminently  suggestive  of  the  progressive  develop- 
ment of  simple  into  complex  markings  by  some 
selective  agency,  seem  to  be  unexplained  by  any  other 


OTHER  THEORIES  OF  SEXUAL  COLOURING       335 

theory.  It  is  impossible  to  understand  how  any  neces- 
sities for  recognition,  any  changes  in  the  internal 
organs,  any  gradually  increasing  vitality,  could  cause 
the  one  form  of  marking  to  develop  into  the  other, 
along  lines  which  correspond  with  the  attainment  of 
a  gradually  increasing  aesthetic  effect. 


336         THE  COLOUES  OF  ANIMALS 


CHAPTER  XVH 

SUMMARY  AND   CLASSIFICATION 

IT  now  remains  to  bring  together  the  results  arrived 
at,  and  to  show  their  relation  to  one  another,  in  a 
system  of  classification. 

I  have  not  introduced  the  terms  proposed  below 
into  the  earlier  parts  of  this  book :  it  appeared  better 
first  to  illustrate  the  meaning  and  use  of  existing 
terms  by  the  description  of  numerous  instances.  I 
trust,  however,  that  the  new  terms  may  be  found  to 
be  useful.  My  friend  Mr.  Arthur  Sidgwick  has  kindly 
helped  me  in  choosing  the  words. 

In  the  following  scheme  Protective  and  Aggressive 
Resemblances  are  grouped  with  Mimicry  under  the 
first  head  of  Apatetic  Colours,  because  an  animal  is 
thus  made  to  resemble  some  other  species  or  some 
other  object.  Protective  and  Aggressive  Resemblances 
are  classed  as  Cryptic  Colours  (Procryptic  and  Anti- 
cryptic),  because  their  object  is  to  effect  conceal- 
ment ;  Mimetic  Resemblance  and  Alluring  Colouration 
are  called  Pseudosematic  Colours,  because  they 
usually  resemble  Sematic  or  Warning  and  Signalling 


SUMMARY  AND   CLASSIFICATION  337 

Colours,  and  deceptively  suggest  something  un- 
pleasant to  an  enemy  or  attractive  to  prey.  While 
Mimetic  and  Alluring  Colours  are  therefore  correctly 
classed  in  the  same  group  with  other  forms  of  Besem- 
blance,  the  terms  suggested  convey  the  relationship  to 
Warning  or  Sematic  Colours. 

The  second  head  (Sematic  Colours)  includes  Warn- 
ing Colours  and  Eecognition  Markings:  the  former 
warn  an  enemy  off,  and  are  therefore  called  Apose- 
matic;  the  latter  assist  an  individual  of  the  same 
species,  and  are  termed  Episematic. 

The  third  head  includes  the  colours  displayed  in 
courtship,  which  are  therefore  called  Epigamic. 

The  vertical  arrangement  in  the  table  indicates 
the  three  chief  divisions  under  which  the  various 
uses  of  colour  may  be  grouped,  together  with  the  sub- 
division of  the  first  into  its  two  main  classes.  But 
the  horizontal  arrangement  is  also  of  importance ;  for 
Pseudaposematic  colours  (I.  B  1)  are  special  and  highly 
remarkable  instances  of  Procryptic  colours  (I.  A  1), 
and  deceptively  resemble  Aposematic  colours  (II.  1). 
Similarly,  Pseudepisematic  colours  (I.  B  2)  are  special 
instances  of  Anticryptic  colours  (I.  A  2),  and  may 
depend  for  success  upon  the  deceptive  resemblance  to 
Episematic  colours  (II.  2). 


